A screenshot of the FireShot extension for Firefox
One note is that it has problems with flash stuff sometimes. I think this has to do with the way the flash engine is does rendering outside of the main application render engine. If you have problems with something another screen capture utility that I use is ScreenGrab.
In its options menu you can choose from using the Firefox render engine or a Java one. If you use Java, it captures the flash elements that are sometimes missed by the the Firefox instance.