On Stack Overflow (and lots of other websites too, unfortunately), Firefox 4 beta (at least versions 4.0b4pre-b6pre) automatically adds a resize handle to text areas, which is probably not what you would want it to do, and it is a bit annoying to have when it obviously shouldn't be there.
This is most likely because the
resize CSS property for text areas is set to
both by default in HTML text areas in Firefox 4 beta, instead of
none, like most other browsers.