Well, I asked whether this could be done, and got answered that extensions exist for that. You can try the Webpanel Enhancer and the Content Holder. They don't work exactly as with Visual Studio, but this is a start.
The author of the Content Holder extension is Hiroshi Shimoda who is also the responsible for the must-have Tabbrowser Extensions.
If you wonder about Firebird or are a frequent user or simply a developer, I advise you have a look to the available extensions. Many of them are very useful for web developers. Mozilla is not only a web browser, it's also a development platform...
BTW, if you heard about XUL and want to see what can be done with it, you can try the Mozilla Amazon Browser.
Also note that Cameron has posted a positive review of Firebird after re-evaluating it.