I've been using Firefox 3 now for the past day on both my Mac and Windows computers. I used to use Safari beforehand and am desperately missing Inquisitor - perhaps I'll find a similar extension or it's built in and I haven't realised.
So far I like the native widgets so it's aqualicious in Mac OS X which is nice - but you don't get the fancy Cocoa textbox facilities (spell as you type, built in dictionary lookup, etc) which Safari offers. I don't like the big "back" button, but luckily I discovered "use small icons" in the toolbar customisation which keeps it the same size as the rest. I've installed the del.icio.us extension which I used regularly with FF 2 on Windows, unfortunately it doesn't use the losenge shaped buttons on Mac OS X which makes the toolbar appear a little odd.
As a thank you, Mozilla are offering certificates to those who downloaded which is cool!