Another FF user here. I also like AdBlock, FlashBlock, NoScript, and a few other ones. But I sometimes use Safari when it is too difficult to figure out why FF won't access a site, usually because I have it nailed shut from so much 'stuff.' And I much prefer Safari's use of the System graphics for buttons, lists, etc.
Still use Eudora for email, haven't been tempted to use anything else. It works, I know how to use it, so does my wife, etc.
No matter what browser you use, I highly recommend 1PassWord for entering and storing your personal info and passwords.
BTW, I think you can get 1PassWord free for a while!
And I wouldn't run an email program without SPAMsieve!
As for importing address books, etc., you may have to work at it from the other end. In other words, you may have to search for a way to
export that info from your current app in a form that can be used by the new one. Don't know what export capabilities Mail has.
I guess the point is that all these programs have reached a level of maturity that they seldom crash, corrupt your data, etc. So, it comes down to using what you like after making sure they do things the way you want.