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}

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.

Hi Fred,

Thanks for this - I have worked through the security program and the runtime components, and having gone for a clean install from MS Store, it now seems to work for the time being. Fingers crossed eh?

Cheers, E

Give it a few days. If the problem is gone, Great ! !

If your problem has been resolved, please select the answer that solves the problem. This will help other users with similar problems find the solution.

Thank you for contacting Mozilla Support.

Hi Fred, Sorry to say it has now disappeared again. No idea why it vanished, no sign of it in task manager, and no luck bringing it back by clean re-installing the MS Store version... Grateful for any ideas, as I really don't want to be forced on to Edge - it all feels a bit like an MS plan to kill other browsers, but they wouldn't be able to make that work neither eh?! Cheers, E

Install the version from; Download Firefox For All languages And Systems {web link}

Hi Fred,

Yep - that is where I had been getting the downloads from (apart from the version from the MS Store). I followed your link, and left it as English US (having tried the English UK previously) and while it all downloaded etc, I got two line flashes of blue along the taskbar, then nothing. Likewise, as previously, nothing shows in the Task Mgr either?

Cheers, E

Weird - I just uninstalled the version from your link, followed the MS Store version through and it has now flashed back to life with the same tabs open as when it was last seen... WTF? Glad it's back, but not trusting that it is here to stay!! Grateful as ever for any thoughts! E

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems. Go to that post and click the 'Solved' button to its right.