Shiretoko's setup dates to the beta days, when people wanted to retain Firefox
3.0 for when Shiretoko crashed.

I had 3.5 crash, so I removed it. I was glad I still had 3.0.

If you really want to delete Firefox 3.0, you can probably do it through
Synaptic.

When I installed 3.5, 3.0 was still the browser invoked from links in email....

This might not get "resolved" until Ubuntu 9.10.