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I cannot open firefox, though other internet browsers work.

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  • Last reply by fanesi

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I am unable to access Firefox at all. I click to open the browser, the icon will flash for a couple seconds, then nothing. This happened shortly after an automatic AVG update this morning. I worked with AVG to disable their security, but still nothing. I tried solutions listed on the Mozilla website, with no luck. I cannot reset Firefox to default settings, as I cannot even open it. When looking under Firefox properties on my computer, it does show that it was modified 2 days ago, but don't know what that is about, or who modified it. Another computer in the office had an AVG update also this morning, but I can access Firefox on his computer with no problem.

I am unable to access Firefox at all. I click to open the browser, the icon will flash for a couple seconds, then nothing. This happened shortly after an automatic AVG update this morning. I worked with AVG to disable their security, but still nothing. I tried solutions listed on the Mozilla website, with no luck. I cannot reset Firefox to default settings, as I cannot even open it. When looking under Firefox properties on my computer, it does show that it was modified 2 days ago, but don't know what that is about, or who modified it. Another computer in the office had an AVG update also this morning, but I can access Firefox on his computer with no problem.

All Replies (6)

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It is possible that your security software (firewall, anti-virus) blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:


Can you start Firefox in Safe Mode by holding down the Shift/Options key?

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Thanks for your quick reply, cor-el. I work in a busy office and was not able to try your suggestions right away. I have tried your suggestions, some prior to your email, with no luck. I even tried changing my firefox settings to run the program as an administrator, and each time it would ask me to allow firefox to make changes to my computer. I said yes and it seemed to take changes, but each time I tried to get into the program, it would give me the "allow to make changes?" flag again and again. I did a compatibility scan on my firefox program, which said it was an incompatible application. I reset to use the prior firefox version from Feb 2014, but it still wouldn't open, and came up incompatible application again. If I need to, I can remove firefox from my computer and reinstall, but my big concern is my bookmarks, saved logins, etc. Any further suggestions? Thanks so much for your help.

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Check that Firefox isn't set to run as Administrator. Right-click the Firefox desktop shortcut and choose "Properties". Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

  • Privilege Level: "Run this program as Administrator" should not be selected
  • "Run this program in compatibility mode for:" should not be selected

Also check the Properties of the firefox.exe program in the Firefox program folder (C:\Program Files\Mozilla Firefox\).


You can do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

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

If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software.

  • Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you lose personal data like bookmarks and passwords from profiles of other Firefox versions.

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

  • (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
  • (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.


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Hi cor-el, finally found time to follow your most recent instructions. I checked the properties to make sure the privilege level and compatibility were as you instructed, but still no luck. I then downloaded a fresh Firefox copy and saved it as instructed. Unfortunately I was not able to uninstall my prior version of Firefox. I was in the Uninstall Wizard but it would not let me past the first screen. It kept on saying "Please close Firefox to continue." I didn't have Firefox open anywhere, at least as far as I could see. As I mentioned in an earlier email, my Firefox icon on my taskbar flashes as if it is being opened, but never opens. Maybe it is opening, but I am not able to see it?

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If you aren't able to uninstall Firefox then this could be an indication that your security software is causing this problem.

Try to boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if this helps.

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Hi cor-el, I got it resolved by contacting AVG again. The woman I spoke with knew the right questions to ask. It turned out there was an old anti-virus software that was not uninstalled by the IT person when he installed AVG a few years ago. I uninstalled that old program, which allowed me to access Firefox. (Odd that my inability to get into Firefox happened immediately after the AVG update.) Anyway, problem solved. Thanks so much for your time and help!