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Since upgrading to FireFox 6 I cannot run Firefox in Avast Sandbox - get error "This application has failed to start because xul.dll was not found". Firefox works fine outside Avast Sandbox.

  • 5 replies
  • 13 have this problem
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  • Last reply by dave_sox

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The error box is entitled firefox.exe - Unable To Locate Component. It suggests re-installing may fix the problem but I've un-installed and re-installed firefox a number of times and no change.

The error box is entitled firefox.exe - Unable To Locate Component. It suggests re-installing may fix the problem but I've un-installed and re-installed firefox a number of times and no change.

Chosen solution

problem is Firefox works outside of the Avast sandbox but, inside the sandbox, xul.dll file is not found

Resolved it with these steps... some may be unnecessary 1) uninstalled Firefox 2) downloaded current version of FF (6.02) and installed 3) opened Avast user interface > Additional Protection (in Avast v6) > Sandbox > Expert settings (Button) > Web Browsers > (under maintenance) "delete contents" (button) 4) logged out of Windows 5) logged in and Firefox started in sandbox

It could be that the first 2 steps are not required... but that's what I did and the problem was fixed. As you can see in the screen shot, Firefox is successfully virtualized

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Download a fresh Firefox copy and save the file to the desktop.

  • Uninstall your current Firefox version.
  • Do not remove personal data when you uninstall the current version.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

  • It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.

Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

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Sorry for the delay in getting back on this. I've tried what you suggested, but it's not made any difference. The xul.dll file is definitely there after re-installing, but I'm still getting the same error.

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Make sure that AVG isn't preventing Firefox from installing an updated (version) of that XUL.DLL file.

You did remove the Firefox program folder (C:\Program Files\Mozilla Firefox\) to be sure that AVG doesn't still may keep copies of the files in that folder?

Try to disable the AVG Sandbox while uninstalling and reinstalling Firefox.

If you still have problems then try to ask advice in the AVG forum.

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Chosen Solution

problem is Firefox works outside of the Avast sandbox but, inside the sandbox, xul.dll file is not found

Resolved it with these steps... some may be unnecessary 1) uninstalled Firefox 2) downloaded current version of FF (6.02) and installed 3) opened Avast user interface > Additional Protection (in Avast v6) > Sandbox > Expert settings (Button) > Web Browsers > (under maintenance) "delete contents" (button) 4) logged out of Windows 5) logged in and Firefox started in sandbox

It could be that the first 2 steps are not required... but that's what I did and the problem was fixed. As you can see in the screen shot, Firefox is successfully virtualized

more options

I just did from step 3 onwards and this worked - thanks

3) opened Avast user interface > Additional Protection (in Avast v6) > Sandbox > Expert settings (Button) > Web Browsers > (under maintenance) "delete contents" (button) 4) logged out of Windows 5) logged in and Firefox started in sandbox