My last post was about a little Greasemonkey script that I wrote to keep my last.fm window open from accidental closings. I thought it would be cool if there was an extension that could handle this, so before building one, I browsed the Firefox extensions for one.
I found one that did everything my little script did and so much more: Tab Mix Plus.
All you have to do with this extension is right click and select 'Protect this Tab' and 'Lock this Tab.' The 'Protect' keeps you from closing the window, and the 'Lock' locks in the current URL, forcing links on that tab to open up in new tabs. Useful.