Firefox Mobile for N900 is fine upto a point , it is still in it's beta stage and developers are working on it hard ...

They have improved quite much since it's previous beta's , the browser was more jamming kind of in it's old beta ... since there it's become much smoother ... yes ofcourse still can't be as smooth as MicroB or Opera .

I use it to test out new and Featured Add-ons , it is improving much quicker