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Since few days Firefox doesn't start in my user account anymore. A clean reinstallation die not solve the problem.

  • 7 replies
  • 1 has this problem
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  • Last reply by John Doe

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Hello, since few days the Firefox browser doesn't start in my user account. If I switch to the other account (Administrator) it start as normal.

Double click to the Firefox icon shows for just few milliseconds a small window but can't see what it means. No task appear in windows task manager. MS Firewall is not blocking the Firefox. No entry in Windows Event log

What did I try to fix the problem. - update Firefox to the latest version (from 90.x to 91.0) under Admin account - clean up Firefox - deinstalled Firefox and install an older version eg. 89.0 - removed all user related data (Firefox) under %APPDATA%\Mozilla\ - install the current version (from Mozilla website) - tried to start in safe mode - check for Maleware - run deep scan Antivirus (Microdoft Defender) - add the user to administrator group

Firefox 91.0 OS Windows 10 prof. (all current available updates installed)

MS Edge is running normal.

Is there someone who have had same trouble and found a solution?

Hello, since few days the Firefox browser doesn't start in my user account. If I switch to the other account (Administrator) it start as normal. Double click to the Firefox icon shows for just few milliseconds a small window but can't see what it means. No task appear in windows task manager. MS Firewall is not blocking the Firefox. No entry in Windows Event log What did I try to fix the problem. - update Firefox to the latest version (from 90.x to 91.0) under Admin account - clean up Firefox - deinstalled Firefox and install an older version eg. 89.0 - removed all user related data (Firefox) under %APPDATA%\Mozilla\ - install the current version (from Mozilla website) - tried to start in safe mode - check for Maleware - run deep scan Antivirus (Microdoft Defender) - add the user to administrator group Firefox 91.0 OS Windows 10 prof. (all current available updates installed) MS Edge is running normal. Is there someone who have had same trouble and found a solution?

All Replies (7)

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Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

  • Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
  • Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

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Have done the task according the instruction (also behind the link) three times but no changes in Firefox behavior. It doesn't start like described before.

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Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.


Download Firefox For All languages And Systems {web link}

Firefox ESR; Extended Support Release {web link}

Beta, Developer, Nightly versions https://www.mozilla.org/en-US/firefox/channel/desktop/

Install Older Version Of Firefox {web link}


Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

How to Start all Computers in Safe Mode; {web link} Free Online Encyclopedia

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You can check for issues caused by a corrupted or incomplete Visual C++ installation that is missing runtime components (Redistributable Packages) required by Firefox, especially VCRUNTIME140_1.dll.

See "Visual Studio 2015, 2017 and 2019":

You may not need the latter (32-bit version) if you use 64-bit Firefox. You may have to reboot the computer.

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@ FredMcD I remove the Firefox installation also all folder and from both user too. Cleaned up registry from "Mozilla" and "Firefox" keys. Dowloaded the current Firefox 64 bit (German) version from mozilla.org for new clean installation. On the end I have reboot the computer.

@ cor-el I have done the installation for 64 bit version as descriped and reboot the computer.

After both things I have done clicked first time to start the Firefox as normal user. The browser was starting as normal. After I have closed the browser, it was not possible to start Firefoy as normal user.

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Did you try another reboot ?

You can boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

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Hi, it tooks a while to get the normal user to the safe mode because he wasn't in Administrator group. After I was able to start in safe mode as my normal user it was also possible to start the Firefox. Have tried this few times. After restart the computer in normal mode it's still not possible. Now I know it will start in safe mode but don't know to find out the reason which make the trouble.