XPCOM
Moderators: Support Staff², Support Staff, AvantGuard, Developer
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- AvantGuard
- Posts: 1966
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Re: XPCOM
Do you mean when you try to use the Firefox engine in Avant?
There should be an xpcom.dll file in your \Avant\gecko\ folder. Check to see whether it's there.
Also, this error is frequently caused by add-ons, especially toolbars. Try temporarily disabling all your add-ons, and if the problem goes away, re-enable them one at a time until the problem comes back to determine which one is causing the error.
Please read this post: http://forum.avantbrowser.com/viewtopic ... 13&t=32497.
There should be an xpcom.dll file in your \Avant\gecko\ folder. Check to see whether it's there.
Also, this error is frequently caused by add-ons, especially toolbars. Try temporarily disabling all your add-ons, and if the problem goes away, re-enable them one at a time until the problem comes back to determine which one is causing the error.
Please read this post: http://forum.avantbrowser.com/viewtopic ... 13&t=32497.
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- Avantic
- Posts: 942
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- Avant Version: 2016 utimate latest
- Default engine: Firefox
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Re: XPCOM
I'm guessing. What version of Windows do you have? There may be some problem with Firefox under Windows XP.wchillman wrote:When I try to use the Firefox browser I get a pop-up that says it can't load XPCOM? Any ideas?
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
I doubt that XP has anything to do with this. I run Avant with the Firefox engine for many hours a day on XP (32-bit), and I've never seen this error or heard of anyone seeing this error only on XP. The Firefox engine actually works much better than either the Chrome or IE engines on 32- bit XP, largely because Firefox uses a lot less memory than the Chrome and IE engines, and 32-bit XP can only access approximately 3.5 GB of RAM total. The only problems I'm seeing with the Firefox engine are somewhat frequent firefox.exe crashes, which many other users are also experiencing on Windows 7 and Windows 8 in addition to XP. The only other problems I experience specifically with the Firefox engine are websites that are coded in such a way that they only work properly with IE (and possibly Chrome, but I almost never use the Chrome engine).
Also, we still need to know whether wchillman meant that he or she is having trouble with the Firefox engine under Avant or the actual Firefox browser, which is what it says in his/her post.
Also, we still need to know whether wchillman meant that he or she is having trouble with the Firefox engine under Avant or the actual Firefox browser, which is what it says in his/her post.
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- Semi-Fan
- Posts: 79
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- Windows Version: Windows 7 Lite x64
- Avant Version: 2012 Build 197
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Re: XPCOM
This happened to me only when i was playing with .dlls overwriting them and trying to update the engine manually. So you probably got wrong version of some dll or corrupted, if it isn't missing. Re-download another version and/or reinstall.wchillman wrote:When I try to use the Firefox browser I get a pop-up that says it can't load XPCOM? Any ideas?
- DutchGemini
- Avant Fanatic
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- Location: Lake Maggiore - Italy, just below the Swiss border
Re: XPCOM
I have the same problem since I upgraded [automatically] to Ultimate 2013 Build 110 last week, before I never saw this error.
My configuration runs AB with 5 additional pages at startup, and was using FF as the rendering engine.
Since 2013b110 none would open and AB would not even load.
I have changed the rendering engine to Chrome and the problem is now solved, were it not that when I quit AB, I get twice
this pesky MsgBox about FF not being able to open XPCOM. Since I do not use FF as a rendering engine, why do I get these messages anyway?
I do not have Chrome or FF installed as native Browsers (never installed), only AB and use Chrome/FF gecko engine in it. I do have Thunderbird 17.0.4.
Running W7x64.
Dutch
My configuration runs AB with 5 additional pages at startup, and was using FF as the rendering engine.
Since 2013b110 none would open and AB would not even load.
I have changed the rendering engine to Chrome and the problem is now solved, were it not that when I quit AB, I get twice

I do not have Chrome or FF installed as native Browsers (never installed), only AB and use Chrome/FF gecko engine in it. I do have Thunderbird 17.0.4.
Running W7x64.
Dutch
- DutchGemini
- Avant Fanatic
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- Location: Lake Maggiore - Italy, just below the Swiss border
Re: XPCOM
Nope, not found "xpcom.dll"mbrazil wrote:There should be an xpcom.dll file in your \Avant\gecko\ folder. Check to see whether it's there.
Dutch
- DutchGemini
- Avant Fanatic
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- Avant Version: Always the Latest
- Default engine: Chromium
- IE Version: 11.0.9600.18282
- Skin: Aluminum
- Location: Lake Maggiore - Italy, just below the Swiss border
Re: XPCOM
XPCOM.DLL may be missing in the installation of AB (under "Program Files\Avant Browser\gecko") because of the problem mentioned in the next URL, which is indeed the release of the FF engine (v22) included in Ultimate 2013 b110:
http://support.mozilla.org/en-US/questions/955040
http://support.mozilla.org/en-US/questions/955040
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
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- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
Search your hard drives for xpcom.dll, and if you find any, post the sizes, creation dates, and locations of them.
You might be able to fix the problem by downloading the USB version of Avant, and after unpacking the files, copy the gecko folder from the USB version to the Avant program folder, overwriting the existing gecko folder.
Another possibility, if xpcom.dll is actually there, is that your security software is not allowing it to load.
As a possible temporary fix for the xpcom messages when you have Chrome set as your default engine is to rename the gecko folder in your Avant program folder. If Avant doesn't see the gecko folder, it shouldn't look for any of the files that are supposed to be in it.
You might be able to fix the problem by downloading the USB version of Avant, and after unpacking the files, copy the gecko folder from the USB version to the Avant program folder, overwriting the existing gecko folder.
Another possibility, if xpcom.dll is actually there, is that your security software is not allowing it to load.
As a possible temporary fix for the xpcom messages when you have Chrome set as your default engine is to rename the gecko folder in your Avant program folder. If Avant doesn't see the gecko folder, it shouldn't look for any of the files that are supposed to be in it.
- DutchGemini
- Avant Fanatic
- Posts: 355
- Joined: Wed Jan 28, 2004 8:10 am
- Windows Version: 2000, XP, Vista, 7 (32/64bit)
- Avant Version: Always the Latest
- Default engine: Chromium
- IE Version: 11.0.9600.18282
- Skin: Aluminum
- Location: Lake Maggiore - Italy, just below the Swiss border
Re: XPCOM
Found only 1, located under Thunderbird's folders, version 17.0.8.4961 timestamped by Mozilla on 02/Aug/2013 01:25:22. I have copied this DLL to the 'gecko' folder without solving the problem, tried to registr it but it gave errors cuz' probably it is linked to another DLL that I did not copy and I have no desire to do a dependency check on XPCOM to see which one is missing.
I still do not understand why, setting Chrome as the default engine and NOT using another engine in one of the pages opened (especially not FF), when I shut down Avant I get the error message [from FireFox] twice. This p!sses me off...
I still do not understand why, setting Chrome as the default engine and NOT using another engine in one of the pages opened (especially not FF), when I shut down Avant I get the error message [from FireFox] twice. This p!sses me off...
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
Have you tried reinstalling Avant? If so, have you tried uninstalling and then reinstalling Avant?
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- Avant Fanatic
- Posts: 398
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- Windows Version: W10 x64 / W7 x64
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- Default engine: 1ºFirefox \ 2ºChrome
- IE Version: 7 and 10 but i never use it
- Skin: Xito - old skins
Re: XPCOM
I dont have any xpcom.dll file in the avant install folder or in the avant profiles folder , and no problem here , but i use xp .
I have posted a request sometime ago , to avant just clear the records of the engines that we use .
Uninstall and reinstall avant again , you can also try use a new profile just to test (backup your old profile first) .
You can rename the gecko folder to other name and probably you will not have that problem , but then you will not be able to use firefox rendering ever again .
( I have the webkit folder renamed , i "never" use chrome rendering , i just use it when i spend long time using Google maps , chrome rendering load the maps faster than firefox rendering . )
Other thing you can try is , if theres some extensions in the firefox rendering addons , disable all and see if works .
When we close avant , avant may launch firefox.exe to clear some records (or all) , even if you dont use firefox rendering .DutchGemini wrote: I still do not understand why, setting Chrome as the default engine and NOT using another engine in one of the pages opened (especially not FF), when I shut down Avant I get the error message [from FireFox] twice. This p!sses me off...
I have posted a request sometime ago , to avant just clear the records of the engines that we use .
Uninstall and reinstall avant again , you can also try use a new profile just to test (backup your old profile first) .
You can rename the gecko folder to other name and probably you will not have that problem , but then you will not be able to use firefox rendering ever again .
( I have the webkit folder renamed , i "never" use chrome rendering , i just use it when i spend long time using Google maps , chrome rendering load the maps faster than firefox rendering . )
Other thing you can try is , if theres some extensions in the firefox rendering addons , disable all and see if works .
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
xpcom.dll is kept in the gecko folder, not in the Avant program folder or the Avant Profiles folder. The Firefox engine cannot run without xpcom.dll.
The xpcom error is unlikely to be caused by a damaged profile, but renaming the Avant Profiles folder as a test is worth a try.
If you rename the gecko folder, you won't be able to use the Firefox engine while the folder is not named gecko. If you rename it back to gecko, the Firefox engine will work again (once the xpcom problem is fixed). The gecko folder will also be recreated the next time an Avant update is installed, so you'll be able to use the Firefox engine again at that time as well.
You can only disable any Firefox add-ons when the Firefox engine is running, and with the xpcom problem, it can't run. You can uninstall (but not disable) Firefox add-ons if they are listed in Windows' Add or Remove Programs.
The xpcom error is unlikely to be caused by a damaged profile, but renaming the Avant Profiles folder as a test is worth a try.
If you rename the gecko folder, you won't be able to use the Firefox engine while the folder is not named gecko. If you rename it back to gecko, the Firefox engine will work again (once the xpcom problem is fixed). The gecko folder will also be recreated the next time an Avant update is installed, so you'll be able to use the Firefox engine again at that time as well.
You can only disable any Firefox add-ons when the Firefox engine is running, and with the xpcom problem, it can't run. You can uninstall (but not disable) Firefox add-ons if they are listed in Windows' Add or Remove Programs.
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- Avant Fanatic
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- IE Version: 7 and 10 but i never use it
- Skin: Xito - old skins
Re: XPCOM
mbrazil wrote:xpcom.dll is kept in the gecko folder, not in the Avant program folder or the Avant Profiles folder.
I said "in the avant install folder" as a whole (all files and folders inside of avant install folder , gecko and webkit files included and all the other folders too , all) .Crazy_John wrote:I dont have any xpcom.dll file in the avant install folder
Looks like it can run , i dont have that file in avant installation folder (all that is inside of the folder and all the other folders too) and is working very well .mbrazil wrote:The Firefox engine cannot run without xpcom.dll.
I dont have any extension installed that is in the add\remove programs of xp .
Here in my pc is possible remove all extentions without have firefox rendering running , go to avant profiles search for the extensions folder that is in the gecko folder (search) , delete all that is inside of the extensions folder .
DutchGemini can give it a try and see if its a problem of extensions or not (do a full backup of your avant profiles first) .
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
I did some checking on the xpcom situation. xpcom.dll has been part of every version of Firefox and gecko for years, and every build of Avant 2013 from build 23 through build 109 included xpcom.dll in the \Avant Browser\gecko\ folder (I haven't checked any builds prior to 23 or any builds of Avant 2012). However, Avant 2013 build 110 does not include xpcom.dll. Apparently, something was changed in build 110 so that it is no longer necessary or has been replaced by some other file.
wchillman, who started this thread, doesn't say which version of Avant he's using in either his post or his profile, so we'll have to wait until he returns to the forum to find out which version of Avant he's getting the xpcom error with.
DutchGemini, you shouldn't be getting the xpcom error if you're running build 110. I wonder if one of the recent Avant updates didn't install properly and you ended up with a mix of files from more than one build. I think your next step should be to uninstall Avant, download build 110 again, and reinstall it. Before reinstalling build 110, check the Avant Browser program folder to make sure nothing other than your Avant Profiles folder is left behind.
wchillman, who started this thread, doesn't say which version of Avant he's using in either his post or his profile, so we'll have to wait until he returns to the forum to find out which version of Avant he's getting the xpcom error with.
DutchGemini, you shouldn't be getting the xpcom error if you're running build 110. I wonder if one of the recent Avant updates didn't install properly and you ended up with a mix of files from more than one build. I think your next step should be to uninstall Avant, download build 110 again, and reinstall it. Before reinstalling build 110, check the Avant Browser program folder to make sure nothing other than your Avant Profiles folder is left behind.
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- Avantic
- Posts: 942
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Re: XPCOM
It may be completely irrelevant, but I looked for xpcom.dll in my computer. I did find something with that name, but it was among the files of Libre Office 3.5. It has no connection with either Firefox or Avant.
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
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- Location: Grass Valley, CA
Re: XPCOM
If you have only build 110 installed, or if you're running the Lite version (or both), it's normal not to have xpcom.dll on your system. It used to be installed with every version of Ultimate through build 109, but starting with build 110 it's not there anymore.mathman wrote:It may be completely irrelevant, but I looked for xpcom.dll in my computer. I did find something with that name, but it was among the files of Libre Office 3.5. It has no connection with either Firefox or Avant.
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- Avantic
- Posts: 942
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Re: XPCOM
Avant 110 ultimate. Firefox 23.0. (just got updated to 23.0.1) are my current versions.mbrazil wrote:If you have only build 110 installed, or if you're running the Lite version (or both), it's normal not to have xpcom.dll on your system. It used to be installed with every version of Ultimate through build 109, but starting with build 110 it's not there anymore.mathman wrote:It may be completely irrelevant, but I looked for xpcom.dll in my computer. I did find something with that name, but it was among the files of Libre Office 3.5. It has no connection with either Firefox or Avant.
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- AvantGuard
- Posts: 1966
- Joined: Tue Jul 26, 2005 10:04 pm
- Windows Version: 10
- Avant Version: 2015 Ultimate Build 28
- Default engine: Gecko (Firefox)
- IE Version: 10
- Skin: Monai XP
- Location: Grass Valley, CA
Re: XPCOM
Yep, it's no longer part of Firefox either in ver. 23. Mozilla must have migrated its functions into one of the other files.
- DutchGemini
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[SOLVED] Re: XPCOM
Problem appears to have disappeared in build 112 (and 113 to which I upgraded this morning) and I believe this is because of the newer FF engine (v23).