Two additional pieces of information:

• Chrome based browsers (Edge and Brave) work normally
• Virus/malware scans are negative

Also, Firefox troubleshooting information for version 101 has been captured and is available if it will help.

Steps to replicate, screenshots, and websites would help us help you.

Clarification: After updating to version 100 or higher, Firefox loads and displays its normal toolbars and a blank page (expected behavior). Attempting to load any website fails without altering the blank page or generating any error messages. After an initial attempt to load an arbitrary webpage, behavior is somewhat inconsistent (may depend on Firefox version) ranging from unresponsive to being able to select items from the Firefox menu or bookmark toolbar. For example, I've usually been able to enter Trouble-shooting mode from the menu. However, selecting Settings from the menu usually fails to load the settings page. (As noted in the first post, everything works normally in Trouble-shooting mode.)

Firefox 77.0.1 (x64) was installed on this laptop when it was originally setup. Firefox has been routinely updated using the built-in updater. The updater is set to notify when updates are available rather than automatically installing them. Firefox was updated to version 99.0.1 on 14 April 2022 and worked normally. It broke when version 100.0 was installed on 8 May 2022. To recover from the failure (after attempting Refresh, etc.), I uninstalled Firefox, rebooted, and installed version 100.0 (x64) from the Mozilla Firefox downloads page (retrieved with Brave browser). This installation reproduced the original failure observed during the previous update to version 100.0. At that point, I uninstalled Firefox again, removed all profiles, and installed version 99.0.2 (x64). (Mozilla's repository should be easier to find.) Subsequent attempts to update to newer versions of Firefox, 100.0.1 & 101.0, using the built-in updater, basically reproduce the failure observed with Firefox version 100.0. I've installed version 99.0.2 three times now; it works normally. (On the 2nd & 3rd installs, I just let it create new profiles instead of removing the old profiles.)

Obviously, staying in this test and revert loop is time-consuming. When I have a block of time available, I'll let it update to the latest version and do a screen capture if it fails again (not that I expect a screen capture to be very informative).

Hmm, the most common reasons for Firefox to be nonfunctional from the address bar down are either:

(A) The VCRUNTIME140_1.DLL file is missing from where Firefox expects to find it. Seems unlikely if older versions work fine, since this is not a recent dependency.

(B) "Anti-exploit" software that injects into Firefox processes causing a deadlock or crash of the web content processes used to render tabs. This issue could be version dependent if your security software hasn't updated to adapt to changes in recent releases of Firefox. Within the past year, both Malwarebytes Anti-Exploit and Webroot security software have briefly caused that problem, but I'm not aware that they have an issue with Firefox 100 or 101.

But those are external factors and you said:

• Version 100 and higher work correctly in trouble-shooting (safe) mode

So that could point to something else disabled in Firefox's Safe/Troubleshoot mode such as:

• Hardware acceleration of graphics
• JavaScript compilers
• optional userChrome.css/userContent.css customization files

On that first one, you could try disabling Firefox from using hardware acceleration. This is a potential workaround for incompatibilities between Firefox and your graphics card/chipset driver software. This article describes where to make that change: Firefox's performance settings. This will take effect the next time you exit Firefox and start it up again. Any difference?

Since hardware acceleration improves the appearance of fonts and animations, you may want to check whether graphics card/chipset driver updates are available for your system. This article suggests safe ways to do that: Upgrade your graphics drivers to use hardware acceleration and WebGL.

Thanks. I'll give that a try and report back (probably not today). Are you aware of any issues related to Microsoft's Exploit Protection Settings in Windows 10?

Did you also try Firefox 101.0.1 ?

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Are you aware of any issues related to Microsoft's Exploit Protection Settings in Windows 10?

I have never looked at those myself, but unless you changed them from their default settings, they probably are not an issue.

My initial attempt to disable hardware graphics acceleration after updating to Firefox version 101.0.1 didn't help. However, reviewing Windows log files revealed that an service called the AMD Crash Defender started issuing error messages about a month before the initial attempt to update to version 100. It may not be related, but I'm going to take a look at the graphics drivers next.

Firefox version 102.0.1 is working normally. I don't know if the issue was solved by the new version of Firefox or by some other system change, e.g., Microsoft Windows updates.