I saw a Lifehacker blog post today in my RSS reader on this Firefox extension, took one look at the screenshot, and went "Woooooow, give me some of that". Aforementioned Firefox extension: Tab Groups extension for Firefox.
As its name suggests, it allows you to group your tabs in, er, groups. Forget the verbiage, just look at the screenshot:
This extension is a godsend for those of us who usually have a bazillion tabs open in Firefox (personally I keep it under a bazillion tabs so all those tabs don't slow Firefox down - I usually start killing tabs once I hit 30). By allowing you to group your tabs into logical groups, such as one group for work, one for play, and one for your many Gmail accounts, it brings some order to the "tab hell", which usually happens when you have to scroll or Ctrl/Cmd-Tab through more than 20 tabs to find the tab you want. Some people may use an Expose-style extension to show thumbnails of all their tabs at once, Showcase is one example - those are quite nifty as well though I've always found them to be unmanageably slow when there are too many tabs, which kinda defeats the purpose.
Anyway, coming back to Tab Groups extension... This is an extension that's going to be absolutely necessary for those of us who like having many tabs open at once. For those of you who are less tab-crazy, or even, god forbid, surf in single tab mode, I'd expect you'd be much less excited about Tab Groups.
Tab Groups is pretty much early release software (the author considers it pre-alpha), but it's very much already usable at this stage. You can create groups, rename them, and start dragging tabs into whichever tab group they belong. There are several features that are missing but almost definitely planned for future releases. For one thing, you can't move tab groups around, but I'm sure that'll be baked in soon enough. Also, the tab selector (the dropdown list of tabs thingie on the extreme right of your tab bar) stops working if tab is in another group. Another thing is the Ctrl/Cmd-Shift-T to reopen closed tabs currently reopens tabs in a new tab group. All small inconveniences (that would be soon be removed once Tab Group history gets baked in) for a very nice extension.