Additionally to what everyone said already, I have two other uses:

1) I have a set of bookmarks specialized for search. Chrome can do this without bookmarks, but Firefox needs them. I'm talking about bookmarks like this: https://www.google.com/search?q=%s&tbm=isch

Note the %s in the middle, that's where queries go. When you save this as a bookmark and add a keyword to it ("gg" in my case), you can then search images on Google like this:

- Alt-d (jump to url bar)

- gg fluffy kittens

I have a few dozen of these: Google, G images, G translate, G maps, local maps, Wikipedia English, Wikipedia Czech, various dictionaries, whois, wolfram alpha, grammar check, YouTube, Maven search... You get the idea.

2) A huge curated collection of bookmarks to Java libraries. Something similar to all those awesome-java collections that are lately popping up, but more complete, in my browser, indexed for search and neatly grouped into like a hundred folders.