Just a heads up to those who are interested. Mozilla Firefox 0.9 has recently been released. Upgrading from 0.8 was a bit of a pain, as I found that the old versions of my extensions needed updating, and not all would work. Oh, in case it's not obvious, definitely uninstall 0.8 before upgrading to the new version. Just be sure to export your bookmarks to HTML first.
Another issue I've found is with the popular extension, Tabbrowser Extensions. I was having trouble trying with setting new tabs to open in the background, and I could not find information anywhere applicable to Firefox 0.9. So, curious as I am, I decided to resolve this matter myself.
Enter about:config as your URL, then scroll down to the text browser.tabs.extensions.loadInBackgroundMiddleClick. Double-click on this entry, and then change the value of false to true. This will enable middle-clicking on a link to open that link in a new background tab.
I've posted this information in a few other places to help those not knowledgeable about Firefox's configuration menu. Hope this helps!