Is it crashing or just not opening? Did the browser send a crash report?

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}

The window opens for about a second, then closes. My security program is Sophos Endpoint Security, which is outdated. I probably should take it off. It does not have a list of trusted programs and does not contain a firewall. Also, I don't know if this matters; but I replaced SpywareBlaster with Spybot. As far as my Windows 7 goes, I cannot even open in Safe Mode.

As far as my Windows 7 goes, I cannot even open in Safe Mode.

Web search: https://www.bing.com/search?q=win+7+safe+mode

The problem is in Firefox, not Windows; otherwise I would have posted to a Microsoft forum. When I said, "I cannot even open in Safe Mode," I was answering your first question, referring to Firefox again.

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

Starting Any Computer In Safe Mode (web link) Free Online Encyclopedia

https://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

https://www.digitalcitizen.life/4-ways-boot-safe-mode-windows-10/ +++++++++++++++++++++++++++++++++++++++++++++++ If the problem goes away with the computer in Safe Mode, the problem is with one of the other programs on the system.

As a test, disable your protection programs.

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.

Install both 32-bit and 64-bit "Visual Studio 2015, 2017 and 2019" downloads, (x86: vc_redist.x86.exe and x64: vc_redist.x64.exe) from https://support.microsoft.com/help/2977003/the-latest-supported-visual-c-downloads

You may not need the latter (32-bit version) if you use 64-bit Firefox. You may have to reboot the computer. ++++++++++++++++++++++++++++++++++++++++++++++ In another thread, a user reported that a recent update of Malwarebytes Anti-Exploit (version 415) may be causing symptoms similar to the VC Runtime problem. If you have MBAE, it should have a setting to exempt Firefox. You could test whether that makes any difference.

I tried to open Firefox with Windows 7 in Safe Mode yesterday. It only stayed open a few seconds before closing. I even switched profiles with no luck. It did not even stay open long enough for me to restart it without addons. Just now I uninstalled Firefox and reinstalled the latest version. It behaves just as the old one, showing a box that says that Firefox is already running. Task Manager does not show any Firefox processes. I took that installation off as well.

I called for more help.

Thank you. I just noticed that comment about Malwarebytes. On my Windows 7 I do not have it. Just now I removed my outdated Sophos. Comodo with replace it. With that off I may try a new Firefox installation. A day has passed. I just tried to roll back to an older version. One in the 95 range caused the Blue Screen Of Death. Another in the 96 range would not open, showing the same message that a process was still running.