[Osiris]

Pin Tabs In Firefox

The Google Chrome browser provides access to a feature to pin tabs in the web browser by default. Pinned tabs will be moved to the left side of the tabbar where their tab will be changed to a smaller icon that is showing only the favicon of the website in question. The benefit of this approach is that the tabs take less space in the tabbar while they can still be accessed normally by clicking on them.
Pin Tab is a new experimental Firefox add-on that brings this feature to the Firefox web browser. Yes, there have been some tab managers in the past who also provided that option (like the Faviconize Tab extension), but none looked as promising as the Pin Tab extension.

[Trotter]

Looks like a single extension to do this:
Set Up Space-Saving, Permanent Gmail and Reader Tabs in Firefox - Firefox - Lifehacker