It came up during a conversation with a friend that I use IE7 at work as my browser even though it's mostly Firefox at home - this isn't because Firefox is forbidden internally (some use it and even mention so on their external blogs, especially for testing obviously since things like Silverlight need to work in Firefox), but I try to fully dogfood at work (since I'm on a team asking the rest of the company to do exactly that with our product, and it'd be pretty hypocritical otherwise).
He asked what Firefox-ism's I missed when using IE7 - while control-backspace in the search area is definitely on the list (my nitpick-of-the-day in the past), one I really miss is Firefox including the last title of the page (from its cache) when it's doing the completion list in the address bar:
Imagine trying to find a particular forum thread (yes, I could use the forum search) in my history without the title bit on the right side.
Actually, don't even imagine, here's the IE7 version. Can you tell me what these threads relate to just based on the url? Me neither :)