One feature I like being able to toggle in Firefox is tab thumbnails -- not the ones on the Windows 7 taskbar, mind you. I'm talking about in-browser thumbnails which get displayed when switching tabs. Chrome OS has that snazzy, Cover Flow-style switching interface, but that's not part of the Chrome browser on other OSes.
There are, of course, options available in the Google Chrome Extensions Gallery for those of you who enjoy a visual reminder when looking for that tab you misplaced -- or if you just want a little eye candy!
This one might be the closest the Firefox's built in interface. Tabs Plus presents tab thumbnails in three columns and provides a search box at the top -- which might come in very handy for those of you who open more tabs by the truckload. Multiple windows are supported, and their contents are separated by a horizontal rule. Incognito windows will display as well, provided you've checked the box to allow access.
You can also merge everything you have open into a single window, bookmark everything, and close everything with a single click.
While Tabs Plus is nice, it's static. If you're really jonesing for that animated Cover Flow action, you've got a couple options. The three mentioned here all work the same way: click the browser actions button and a popup window lets you arrow through your tabs.
I don't usually pick on apps for memory usage, but I might make an exception for Visual Tabs. With a modest 13 tabs open, Visual Tabs wolfed down a supersized 240MB memory. That's actually more than Chrome, my tabs, and all my other extensions were using at the time.
The Light version keeps things simple: it's a more lightweight version of what Visual Tabs does with no extended options -- just six background colors to choose from.
TabsPreview, on the other hand, is loaded with options. You're not limited to a simple horizontal flow for your tabs: choose from a grid view, Vista-esque diagonal layout, carousel, or a simple horizontal display with zoom effect. Tabs Preview can also show your closed tabs, and you can set any background color you want and add a linear or radial gradient effect.
There's also a search option and a grouped display which limits the preview display to tabs from a specific domain. Tabs Preview is a very good visual switching extension, but I would like the option to use a popup instead of its own tab -- and I'm also not so keen on the bouncy effect on the toolbar icons in the bottom left.