I have mostly abandoned Firefox and switched to Google Chrome.
Firefox became more and more bloaty and heavy (I admit that adding plugins and such must have helped). But the kicker for me was yesterday evening when I tried to get to a page on Yahoo for a mailing list that I co-manage. After accepting that I might see material only suited for 18+ (I am, really), I saw a glimpse of the list page and then I had to confirm again that I am 18+. And again, and again and... so forth.
In Seamonkey there was no problem, nor in Chrome.