I use FF3, and it imported all settings...although I only have one install of FF on my machine; those who have had problems are those with more than one FF install.
However, no plug ins or addons (Google toolbar included - where I have all my bookmarks) are currently supported.
I played about with it this morning, I like the UI, but PPRuNe looks horrible with all those adverts plastered all over the place (AdBlock Plus is another must have addon).
When Chrome supprots addons, I currently use twenty with FF3, I'll consider switching.