I do know you cant run icetea and sun both. Check synaptic search for icetea
and uninstall it. That should solve the problem. Worked for me.

Thanks - that's what I thought. Wish I knew how the openjdk stuff got
installed in the first place - I didn't explicitly request it.
Probably came down with some updates.

Anyway: removing the openjdk (IcedTea) runtimes didn't change
anything: Firefox still crashes at my usual Java enabled sites.
Removing and reinstalling the Sun Java runtimes doesn't seem to have
made a difference, either. (No Firefox crashes with all the runtimes
gone - but no functionality, either.)

Tried removing / reinstalling the flash plugin, too - the FOSS ones
have given me grief. (I use the "nonfree" Adobe flash plugin.)

Still no luck, and I'm officially baffled. I suppose I could remove
the Sun runtimes, and install the openJDK stuff. But I've had such
bad luck with the IcedTea runtimes in the past.

Any ideas?

As it turns out, the Ubuntu forums have several threads about Java
website failures when using Firefox 3. There's some discussion on
configuring the Sun runtimes vs. the OpenJDK runtimes, Flash, etc.,
but nothing that really applies to my situation (already using the Sun
runtimes, only one version installed, etc). Some contributers
suggested a fallback to Firefox 2, or installing both 2 & 3.

Since I had this working before, I'm concluding that the update from
Firefox 3 Beta to Firefox 3.0.1 introduced a bug.

Not sure if it would help on Linux but this site talk about the problems
about removing Java fragments that it leaves around.

www.raproducts.org

Replying to my own problem with a partial solution. Perhaps it will
help someone else.

I now have most of my favorite Java sites working OK.

The problem was my "Hosts" file ( /etc/hosts ).

I had been using one on my Windows PCs to block advertising sites. I
transferred it to the Ubuntu box and appended it to the /etc/hosts
file generated during installation. Worked just fine during ordinary
web-surfing.

Maybe my "Hosts" file was malformed, maybe it was just too big. Java
sites started working again when I reverted /etc/hosts back to the
"installation" version.