Tabbed Browsing is the most useful feature of FF imo, along with the ability to parse HTML/CSS Correctly,
IE seriously lacks the the parsing domain.
In answer to the first question: its todo with the fact the forum renders things using % of screen width
your resolution is stupidly small, and the "thread icon" thing is too large for silly resolutions, thus it expands the width of the icons layer, but not the background layer, thus the background layer suits your resolution, but the new post, and post-icon bit do not.
@Hate, FF aint a Piece of Crap, its a work of art :P