Hey Mailesel,
I'm the original author of Groove Shredder and just wanted to let you know I am no longer supporting it. Simply put, the people who own it now have disabled my access to the addons.mozilla.org listing so I can no longer update it.
That being said, I have developed a new extension for chrome called RipTide, . I will be probably porting it to Firefox soon.
The new extension doesn't rely on capturing requests to obtain stream keys like Groove Shredder does, so it's a much better experience in my opinion.
I found this post thanks to a Google Alert.