FF 3.5 is sorta like XP to Vista upgrade! A lot of add-on developers have not created 3.5 compatible add-ons, even like compete.com (browser toolbar extension - gives site ranking) has not been updated and for me for SEO purposes it's annoying.
Also, FF 3.5 does not automatically zoom the text as 3.0 did. I'm probably gonna revert to 3.0.
I have a mac mini connected to a 42" LCD TV. When I would load hacker news with 3.0 that version would auto adjust the text to view that was easily readable. Now I have to use more mouse gestures (right click and motion down with mouse) to get that effect and when I go back from reading story back to hacker news I have to do the mouse gestures all over again. Sucks
Also, FF 3.5 does not automatically zoom the text as 3.0 did. I'm probably gonna revert to 3.0.