can be more specific? add on java? for ubuntu, the best way to install java is through synaptic package manager, find package call ubuntu-restricted-extras, it will install MP3 playback and decoding,
support for various other audio formats (gstreamer plugins), Microsoft fonts,
Java runtime environment, Flash plugin, LAME (to create compressed audio files),
and DVD playback.

for more media support, search synaptic for gstreamer0.10-plugins-bad, gstreamer0.10-plugins-bad-multiverse, gstreamer0.10-plugins-good, gstreamer0.10-plugins-ugly, gstreamer0.10-plugins-ugly-multiverse.

basically when u use linux, u cant use windows mentality anymore(well not most of it). its much ezier to get those stuff, no need to download individual stuff unless its not supported by ubuntu n 3rd party in repository. so now, uninstall that silly java u installed! hehe n install those tat i told u through synaptic package manager! im sure your firefox will be back without crashing