What's your computer system and Firefox version? Looks like you are using Windows 10.

Let’s do a full clean re-install;

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Start your Computer in safe mode.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

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

Windows: C:\Program Files C:\Program Files (x86)

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 the profiles folder.

After rebooting the computer, run a registry scanner if you have one. Then run the installer.

I can't boot into safe mode! For whatever reason, it doesn't seem to respond to the F8 key (interesting). I wonder if my Edge issue is also being affected by the same problem? I open edge and it auto-closes after a few seconds.

bxpeters said

I can't boot into safe mode! For whatever reason, it doesn't seem to respond to the F8 key (interesting). I wonder if my Edge issue is also being affected by the same problem? I open edge and it auto-closes after a few seconds.

https://www.techrepublic.com/article/pro-tip-7-ways-to-access-safe-mode-in-windows-10/

Please answer Fred's question, Firefox version please

Expand further on the issue.

I'm trying to install Firefox setup.exe 59.02

None of the normal methods allows me to run in Safe Mode.

bxpeters said

I'm trying to install Firefox setup.exe 59.02 None of the normal methods allows me to run in Safe Mode.

Please search your systems homepage/support or user manual to find out how to boot into Safe Mode if the above URL with 7 ways is not working.

Okay, let's make sure your system is clean.

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

When I want to start my Win 7 in Safe Mode, I press the <F8> key repeatedly.

You can try to create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I'm running Windows Anniversary Edition and was just able to install Firefox .59.02 in Safe mode. However, when launched, I get the same error message about FF already running. Whatever is causing this might also be causing MS Edge to close 15 seconds after opening.

Have you used the malware scanners?

I've just tried 2 malware scanners; no results.

I did easily fix my MS-Edge problem with a simple "repair / reset" in Windows "setting", however.

Do you have any additional possible fixes for this Firefox issue? It seems as though there is an incompatibility with Windows 10 Anniversary edition that needs attention.

• Repair System Registry and Files

Find the Dos Prompt or Powershell : Right Click and Run as Administrator then : Copy/Paste to Dos Window : DISM /Online /Cleanup-Image /RestoreHealth then hit Enter. Reboot when completed. Note : DISM goes up to Microsoft for new files.

I would suggest you update your Win10 as the Anniversary issue is at End Of Life (EOL) You should be on the Creators Update then there was the Fall Creators Update which is version 1709 which you can Find in Settings --> System --> About what your version is. As the Spring Creators update is about to release in 2-3 weeks, in April anyways. you are 2 Windows versions behind and working on 3.

This should be pinned and run weekly : Windows Disk Cleanup. , If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Defrag Monthly.

If you think you have malware go to the pros : https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/

Please let us know if this solved your issue or if need further assistance.

I ran DISM /Online /Cleanup-Image /RestoreHealth and rebooted. This had no effect on my problem. Same Firefox error.

Whenever I experience a Windows-based problem, it's never an easy one to fix. I've been trouble-shooting Windows issues since ver. 3.0 and I've experienced some of the crazies versions of malware / bugs in existence.

Feel free to send any additional fixes you can think of.

Well my suggestion here is uninstall then dive into the registry and delete Firefox and Mozilla entries then reboot. But that is something not recommended here. But this is, uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 59.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.