The folks are updating mozilla constantly. Every 4 hours they create a so called snapshot and make it public so everybody can test that version. Every few weeks/months they freeze the updating, strip all the debug and publish it as Mozilla 1.0 / 1.1 / 1.2 / etc.
Basicly you have the newest version with bugfixes since the Mozilla 1.1 release. It, however, could be slower since there is some dubug information for the develpers in it... and it might crash unexpected if they create a new bug
If you try a nightly build you can see if the problem has been solved... Just to be sure.
Hope things are clear a bit