In Applications folder it's listed as TenFourFox7450 45.6. Is the appended
version number the cause of the problem. If so, that's odd, because I have
always listed the version number, because I keep two or more earlier
versions just in case there are problems with the latest release.
BTW, vers 45.6 is very slow to open and *glacially* slow to close, often
requiring a Force Quit after the viewer window closes and refusing to yield
the menu bar back to the Finder. (?)
As far as the issue with slow to open, 45 in general will be
slower to start than 38, but 45.6 hasn't been any slower on the
test systems than any other version of 45, and I can't reproduce
hanging on quit. Some users have noted some of their addons were
responsible for hangs I couldn't duplicate myself.