If you're a Thunderbird user, and you're always receiving links from friends but can't be bothered opening them in your browser, then this extension could be what you've been looking for. It simply adds URL bar to the Thunderbird interface which allows you to view websites without having to even touch Firefox, IE or whichever browser you use.
The good thing is it's easy to use and unobtrusive because it doesn't require anymore buttons adding to your toolbar because it simply adds it to the message pane that you are reading. if you do want to use your custom browser you can simply right click a link and choose to "Visit in Browser". It's also remarkably customisable for an extension allowing you to configure various Hotkeys with "about:commands" in the URL bar.
The obvious downside is that it is very small. It's often hard to read text and graphics although you can select a full screen mode. Nevertheless, this is an excellent tool for Thunderbird users and will save valuable RAM and productivity time spent reverting back and forth between your browser.