It may be fixed, and if anyone else finds themselves in this nightmare, this is what it took. It seems to have been a real player library which was 32 bit, to which the 64 bit FF 3 was pointing. At least I think this is what nphelix.so is. So, reinstalling FF does not help. This generated all the error messages and segmentation errors.

The smart thing to do on realizing this would just be delete all realplayer files manually from /opt/mozilla.. Now they tell me!

Instead I found a real player uninstall script, which declined to run until it was pointed at /opt, and then simply deleted /opt! Fortunately there was nothing terribly vital in it, just realbasic, and and old copy of openoffice, and who needs them? Well, lots of codecs and stuff, so maybe the problems will show up later on. But at least missing files are fixable.

Then I reinstalled FF again, and it seems to work. There are still sites which it fails to display correctly, but at least it is now, touch wood, not filling the hard drive with xsession error messages.

Peter