Try installing the snap package or the flatpak package and set it as the default browser.

Nice effort to solve the Firefox problem, and I enjoyed reading and following the link, but installing a new snap didn't work. Neither did installing Firefox.deb nor installing from the Firefox download page. All "required libraries" are up to date. The Firefox version did not change nor did its inability to open a link. Firefox opens, then hangs on a blank page. Sometimes the link is shown in the address bar, sometimes not, but it never opens. As I said before, both Chrome and Brave work fine.

Did you change the default browser in Ubuntu Settings > Default Applications > Web? You should see multiple Firefox browsers listed and it may be difficult to tell which one is which.

You can test opening external links by typing a URL in a terminal (Ctrl+Alt+T) then right-click > Open Link.

Thank you for your efforts. Yes, I now have two Firefox browsers, but after update both are version 124.0.2. I can't see why to keep both. Tonight, one browser or another opened three different sites. Then, when I was going to thank you, it wouldn't open this site. The site address was in the window, but the page was blank and remained so. I have tested version 124.0.2 several times since then and it has worked! Perhaps something that you suggested did work. I will give Firefox another try as my primary browser. Finally, an open Terminal in Ubuntu Linux will not give you an "Open Link" option via a right click. We're talking Ubuntu, not Windows. Again, thank you.