--integrating into brower:
search engines (that you select: ggl, az, imdb, wikipedia)
post to dlcs or to blogger

--tabs so can open various things at once easily.
really, it's the one-click 'open in new tab', specifically a click of the scroll wheel middle button of the mouse, that is most happily habitual for me.
and 'bookmark all tabs' option in newer version of firefox, yay, I'd wanted this when saw that reverse (open bkmarks in tabs) was possible.
oh also ability to move tabs around, re-order them in the window. I'd wanted that and now enjoy.

-right click 'search web for' highlighted text

I really like these features, all credit to firefox I suppose. these have ~revolutionized~ the experience of the www for me. it's a very pleasing way of reading-writing. interface.