Bookmark Previews is a Firefox extension, which generates thumbnail previews for all your Firefox bookmarks and lets you browse through your bookmarks in Apple-ish Cover Flow interface.
Basically, this extension adds two views to your bookmark manager: Thumbnail view (Cover Flow style) and Album view. Whenever you add a bookmark or visit any of your bookmarked pages, it snaps a screenshot and preserve it. When you first install this extension, it’ll create thumbnails for your bookmarks in background.
I have around 280 bookmarks in my browser, and I found this extension to be harmful for my browser’s performance. I’m not totally sure, if this is due to the number of bookmarks I’m having, or due to some other reason. Nonetheless, it’s pretty cool, if not very useable.
Bookmark Preview - [via: Lifehacker]

wrote, on June 30th, 2008
Just tried to install this but I get “no preview” on all the bookmarks. Any ideas?
wrote, on June 30th, 2008
Urgh! The issue with lots of these Firefox Plugins and Addons highlighted once again. The browser gets sluggish. Got loads of bookmarks myself, and this app really looks cool, but I need the speed man!
wrote, on June 30th, 2008
Having too many bookmarks does spoil browsing efficiency. I personally just store the sites on a spreadsheet and visit them when I want accordingly.
wrote, on June 30th, 2008
No thanks. I dread to change from the familiar manual way of using the bookmark facility. Even the simple folders system is getting to be daunting in Firefox!
wrote, on July 1st, 2008
Will try it out, a bit worried about the speed but worth a try. Before the FF upgrade I had far too many pluggins and my browser was far too slow, this time round I am going to be more selective.
wrote, on July 2nd, 2008
I guess I will try it out to see how it looks. I dont have much bookmarks(only about 100) so I guess I shouldn’t see a drop in firefox performance because of this.
wrote, on July 2nd, 2008
@Nicole: Adding views without removing the original view is quite ok to me. Looks like a souped-up version of Thumbstrip.
wrote, on July 2nd, 2008
This extension will affect the performance of firefox? If so, I’m not going to use it cos I too have lotsa bookmarks.