Try reinstalling the browser from the OFFICIAL WEBSITE.

Does it still happen in Troubleshoot Mode?

It did still happen in Troubleshoot mode, but I there found out about refreshing Firefox, and that fixed it. I imagine that it was an ad-blocker issue, since at least two of the once-problem pages now have bulky ads that I didn't see before.

 Thanks for pointing me to Troubleshoot mode.

Were you able to submit a crash report with the 64-bit version or were this merely tab crashes (Gah. Your tab just crashed) ?

If you have submitted crash reports, please post the IDs of one or more recent crash reports that start with "bp-".

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the report ID of recent crash reports on the "Help -> More Troubleshooting Information" (about:support).

• click the "All crash Reports" button on this page to open the about:crashes page and see all crash reports.

Alternately, you can open about:crashes via the location/address bar.

See "Viewing reports outside of Firefox":

• https://support.mozilla.org/en-US/kb/mozillacrashreporter

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-crashes-closing-or-quitting
• https://support.mozilla.org/en-US/kb/firefox-crashes-asking-support

All of the crashes were Gah crashes, of one tab after another. I'll be happy to help debug this, but the 32-bit version of FF is serving me adequately.