[Hampshire] Firefox ongoing bother: is it me?

Desktop machine: Ubuntu 8.10, Firefox 3.0.11. Firefox regularly grows
to >1GB in virtual memory size and close to 1GB physical memory at
which point my (1GB) system starts thrashing and I usually need to
kill it and restart. FF version from Synaptic is
'3.0.11+build2+nobinonly-0ubuntu0.8.10.1' which is the up to date
version. It's not a huge Firefox session: 3 windows, 10 tabs. Even
after a fresh restart it shows 250MB resident, 750MB virtual.

Today a new development: used 'killall firefox' at shell prompt and my
X session got killed. Twice.^H^H^H^H^H^HThrice.
I say 'new' because I have not seen this before; but I don't usually
use 'killall' so it may be something that was there all along.

For comparison I am writing this from a laptop 8.04 WUBI installation
(Ubuntu inside Windows), FF is occupying 148MB.