I know it's the best browser on the market, but it's got this smug "Look at me! I'm coded properly! The site you're looking at is not" approach that really appeals to a certain type of user.
Which would be fine if it was actually coded properly - but, like most things designed by Men Who Love Only Pizza And Beard Trimmers, it's surprisingly fussy about things like Flash - as pictures and animation are merely for "those morons who don't use Linux".
Don't get me wrong - the final products are marvellous things, but their rolling development cycle means that Firefox has more unstable releases than a young offender's institute.