After letting it run a while, I came back to a Firefox crash popup saying that (something like) "2020player" had caused problems and the offending page was http://www.washingtonmonthly.com
I assume it was a bad ad or something (which ABP always blocks for me, but maybe the plugin got partially through).
On restarting FF again, I didn't see the problem again, so I guess it was just a coincidence. Looking at Washington Monthly from other PCs hasn't shown any issues (yet).
I'll report back if I have any more information.
Cheers,
Scott.
(Who has had enough issues with Flash and Acrobat Reader that Adobe stuff is his natural first suspicion.)