Update, October 24 (problem persists): Firefox continued to hang upon trying to connect to Google (my go-to test website), and then requires me to Force Quit. Deleted the Firefox app and all Firefox items from the Library, plus a bunch of other legacy items that were empty folders or do not work with Sonoma.

Downloaded and ran trial version of Malwarebytes, found and quarantined one non-dangerous item, but could not launch the Real-Time Protection (solution for that found later).

Following suggestions on Malwarebytes website, I completely reinstalled OS 14.4 (Sonoma) [glad that I had a few hours worth of planting and pruning to do while it installed!], ran Malwarebytes again (found and quarantined a second non-dangerous item), then found a page on Malwarebytes that said the reason I could not launch Real-Time Protection was that I had to give that app full disk access, which I did (System Settings > Privacy & Security > Full Disk Access > toggle on Malwarebytes Protection).

Fortunately Safari works just fine (the Chrome browser also works), which allowed me to download and install a brand new version of Firefox, which immediately proceeded to hang when I tried to go to Google.com. I had to Force Quit the app, which resulted in yet another (now probably over a dozen) crash report to be submitted to Apple.

Hi Julian, was Firefox running normally on your system before Firefox 124/MacOS 14.4, or is this your first installation of Firefox?

Aside from the regular release (so-called rapid release), Firefox has an Extended Support Release (ESR) which is based on a version from last fall. You could download the DMG for ESR and see whether it will install and run normally on your system.

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

Brilliant, jscher2000. Firefox is now working.

To answer your question: I've been using Firefox on Mac OS for years with no problem. In the last few days I did upgrade to OS Sonoma--I do not recall whether Firefox quit working *immediately*, or within a few days. Good call on your part, as that may have been the problem.

I deleted my most recent installation of Firefox and its library, then downloaded and installed the Extended Support Release version of Firefox that you suggested. I tried to visit Google.com, but when Firefox was taking a long time to connect (as happened on every previous attempt) I thought that we had failed once again.

I then stopped the attempt to reach Google and clicked on "About Firefox," where the message said that Firefox was checking for updates. That was taking a long time, so I let the process continue while I left to watch TV for an a couple of hours.

I'm glad that I didn't give up too soon. When I returned after a couple of hours the "About Firefox" window message said that "Firefox is up to date": 115.9.1esr (64 bit)., which I think is the same version I saw when I first launched it, before it checked for updates.

I then imported my bookmarks back from Safari, where I had imported them from Firefox, and now I just to spend a little time checking my Firefox settings. I had also exported my passwords which I'll import tomorrow when I'm fresh.

Thank you again for taking the time to help a tired and frustrated user.

Julian