Here's a late contender for Best Firefox Add-On of 2008: ThumbStrips, which provides thumbnails of your browsing history, making it easy to revisit previously viewed sites.
Actually, this add-on has been around since 2007, but under the radar -- perhaps because it comes from Intuit Labs. Yes, that Intuit. Why they're making Firefox plug-ins is beyond me, but I'm not complaining: ThumbStrips is awesome.
As you browse, ThumbStrips creates a thumbnail of each page you visit and collects them in a filmstrip-style bar at the bottom of the screen. You can scroll through the bar just by moving your mouse to the left or right edge. Click any thumbnail to revisit the page.
By default, ThumbStrips doesn't "record" secure sites, which is extremely smart. Not so smart: You can't relocate the bar to the right or left side of the browser, where most users have extra space. Fortunately, you can minimize and resize the "strip," but I'd still like to see the option to make it a sidebar.
Once you use ThumbStrips for a while, you'll wonder how you ever got along without it. Note to Microsoft, Mozilla, Opera, etc.: Steal this feature! Visual search history should be built into every browser. [via Download Squad]