When I use Google Maps, Firefox uses huge amounts of RAM. If I use
Google Maps enough, FF uses so much RAM that it slows way down and
becomes unstable. Once FF took up 850M of my 1G of RAM, and Google's
JavaScripts started failing.

Closing FF and re-opening it fixes the problem, but then I lose what I
have. Closing the tab with the Google Maps does not help. Is there
something else I can do, e.g. some obscure function which tells FF to
release the RAM it has allocated?