Smart Bookmarks - I'm sure everyone has read what I've read, but it doesn't hurt to write a reminder. Here's a link to UIWeb's "How to build a better web browser" essay: http://www.scottberkun.com/essays/37-how-to-build-a-better-web-browser/
See also: Firefox:History
Relevant research (this is 5 years old but never used!):
Integrating Back, Bookmarks and History - Alternative History Mechanisms for Web Browsers:
http://www.cs.umd.edu/hcil/about/events/history-workshop/slides/Kaasten/ (Online presentation) http://www.cpsc.ucalgary.ca/grouplab/papers/2001/01-IntegratedHistory.CHI/00-IntegratedHistory-CHI.pdf (PDF paper)
If you'd like to describe something you would like to do with Bookmarks, add it to the Bookmarks Use Cases page.
It would be good if the user can see all the favorites of one folder in a strip with a previsualization. This previsualization is updated each time that you visit the page. This previsualization strip will be used with a shift bar to move a small tabselect-window all over these favorites (over the strip). This window will select or highlight only the links/webs that we want to have opened in firefox. That it is to say, when you move the window over the favorite strip one position to the left, one new favorite will be openened and the favorite that is most to the right will be close. The maximum size or width of this window must be configurable, for example 7 tabs. This will save a lot of memory usage in firefox and will let you see all your favorite webs (for example 40) without problem because you will have only 7 web pages opened simultaneously. If this width is reduced from 7 to only 1 what we have is a powerpoint slice "WEB" presentation!!!