There are several possibilities; 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.

By the way, if you are on Windows 10, did you install updates today? Another user mentioned KB5010342 as a potential culprit. However, we don't have much information about that yet, so I think it's premature to try to roll it back.

A couple of other users identified Webroot (security software) as blocking Firefox 97 from running properly:

• https://support.mozilla.org/questions/1367248
• https://support.mozilla.org/questions/1367301

Aha. I do use Webroot so that's what causing it. That explains that then. I don't want to shut off my protection so I'll wait till either Mozilla or Webroot get it patched (hopefully soon).

Thank you everyone - I would have never digured that out on my own.

There is a mitigation for the conflict in Firefox 98, now in beta testing. If you wish, you can confirm by installing Firefox Developer Edition, which will sit alongside regular Firefox and use its own profile folder. https://www.mozilla.org/firefox/developer/

If all goes well with the patch, we can hope it will be added to a Firefox 97.0.1 update. For now, though, I don't have a way to make 64-bit Firefox 97 work with the combination of Webroot plus the recent Windows update.

People are working with Webroot to issue an update.

Until then, a user posted that another workaround would be to run Firefox 97 in backwards compatibility mode. I haven't tested this myself, but here is how you would set that up:

(1) Open the Properties dialog for your Firefox shortcut. Either:

• right-click a Desktop shortcut, then click Properties
• right-click a pinned Taskbar icon, then right-click the Firefox (or Mozilla Firefox) item, then click Properties

(2) Switch to the Compatibility tab

(3) Check the box for "Run this program in compatibility mode for"

(4) If the selector for that option is not set on Windows 8, switch it to Windows 8

As a result of this change, you may notice that some Windows 10-specific features and styling are disabled. However, I am not aware of any major changes. If you experiment with this, let us know your experience.

https://www.mozilla.org/firefox/97.0.1/releasenotes/

Fixed Works around problems with WebRoot SecureAnywhere antivirus rendering Firefox unusable in some situations