I recently ran across FoxGLove:
And I liked the idea, and wanted to try it out. But I have a Mac. No small difficulty--I decided to hack it =]
Here's the screenshot:
I started with Firefox Portable for OS X:
I had to mod it to open while other versions of Firefox are running. After much experimentation, I discovered that you do this by editing the script. Right click on Portable Firefox, click Show Package Contents, open Contents, then Resources, then edit 'script'. Scroll down to the very bottom and you should see a line that says 'quitapp'. Put a hash (#) in front of that line, save the file, and you should be good.
Then I started to install all the plugins and stuff from Alex (the maker of FoxGLove). I had to Google for a couple of them.
I couldn't see how he got Google Talk, Calendar, and Notebook to show up in the sidebar...I didn't see the buttons. So I caved and opened his version in Wine. Three tries later, I had it up and running....and found out that the bookmarks were stuck in the Menu toolbar. Not having one of those on OS X, I improvised and instead put the buttons over the sidebar...where I think they should be anyway. I downloaded the icons from Google and set them up.
Then, I set up Gears to run portably...I installed it in Firefox, then copied the extension over to FoxGLove. It didn't occur to me until afterwards to try to install it regularly....
I downloaded Iconverter to convert Alex's icon to an .icns so I could brand Firefox. I changed the Portable version's icon, and then opened the package and changed Firefox's icon as well....now it just shows Alex's icon, even in the Dock!
The only other thing I would like to do would be to change some more of the Firefox branding to FoxGLove...maybe I'll hack it some more sometime.
You can dowload it right now from http://linuxmercedes.homelinux.com/FoxGLove/index.html.
 Added screenshot. Bonus points to whoever first names the comic on my desktop =]