Firefox only (Win/Mac/Linux): Love the visual tabs in the new Opera 10 Beta but can't leave your beloved Firefox? The Killer Tech Tips blog points out that there's already a Firefox add-on for that.
The Tab Sidebar extension has been around a while, but Killer Tech Tips points out that a quick trip to the add-on's settings panel will let you dock it to the top of the screen, making it work almost exactly like the visual tabs in Opera's latest beta release. The thumbnails include navigation buttons, but you can turn those off in the preferences if you want it to work even more like Opera.
Hit the link for the download, or take a look at the Killer Tech Tips guide for the instructions on setting it up. For another way to visualise your tabs, check out the Tab Scope extension, which gives you a preview window in a mouse-over popup.