It Firefox' Bookmark Dialog you can create a folder or select which folder to file the bookmark in and, even more conveniently, keep that folder in a drop-down menu, as well as other recently used folders.
I also like the Bookmark Stars in the URL bar that indicate if a website is bookmarked, a website can be bookmarked by clicking on the star, but I don't use this feature.
KM
Forum:
Improvement requests