If you're a Last.fm and Firefox user, then the best way to stream radio into your browser is definitely with Fire.fm.
Fire.fm is a small plug-in for Firefox which inserts a wee Last.fm radio player into the top menu bar of Firefox. You can instantly search music on it either by artist name or tags. You also have basic controls such as pause, skip and a volume slider. You can also instantly access recently listened-to artists and search for similar musicians.
The downside of Fire.fm is that since March 30th 2009, free radio on Last.fm has been limited to the United States, United Kingdom and Germany. Anybody outside of these countries has to pay a subscription in order to listen to Last.fm radio. This is beyond the control of Fire.fm, although it will obviously put many users off because the subscription fee is around $3 a month.
For those that can use it however, Fire.fm is the best way for Last.fm and Firefox users to integrate two of their favorite tools.