If you’re having trouble installing Quake Live on Firefox 4 in Linux, don’t fret, there is an easy fix. Download the QuakeLivePlugin_433.xpi. You can download it from the site or here. Once downloaded it open it with Archive Manager and edit the install.rdf. Replace the content in the file with the following:
firstname.lastname@example.org 1.0.433 email@example.com 1.9 2.0.* QuakeLive.com Game Launcher Extension required for play on www.quakelive.com id Software, Inc. true
Save it and open it with Firefox, everything should go as planned. I can confirm it works and is malware\crapware free.