I use tabbed browsing big-time in Mozilla. When I'm reading a page (e.g. my lj friends page), I middle-click on each link I want to read, and then work my way through them after I've done so.
So it infuriates me to no end that the keyboard shortcuts for "close tab" (C-w) and "close browser" (C-q) are so close together. I don't know how many times I've accidentally closed a browser window with 15+ unread tabs in it.
Bleah bleah bleah.