I think that FF (or Fx as the site claims it should be abbreviated to
![LOL :lol:](http://www.tekforums.net/Smileys/teksmileys/lol.gif)
), became so popular because people wanted to get on the MS is evil band wagon, and saw FF as a great way to do it.
This coupled with it being a new browser technology when released meaning few people had found exploits at the time.
More recently it has become popular because of word of mouth, Its safer and faster than IE etc etc.
Just a few points to get started.