Some context: bug 557423 is the main "quake2 is slow" bug, and bug 592833 is a an Audio performance bug that was fixed, originally motivated by quake2. Today I found this Quake2 instance that plays correctly in Firefox, http://crystalin.dyndns.org:8080/GwtQuake.html so I gave it another try in Firefox 10.0a1 / linux x86_64. It's still very slow, around 10-15 FPS but very chunky. Not playable. However, if I set media.ogg.enabled to false (effectively disabling all sound), it becomes a lot faster, above 25 FPS and without the chunkiness. Very playable. A profile really doesn't show much sound-related stuff. Rather, it's mostly JS and OpenGL stuff. There's 2% time spent in libasound.so.
That page consistently crashes my 7.0.1 and nightly (20111005) on Windows: https://crash-stats.mozilla.com/report/index/56226741-b360-430a-b37f-c8c6d2111005
Can you reproduce the crash in Nightly? Just checking if it got fixed by the recent landing of bug 658826. What you're experiencing is a D3D shader linker crash, and in bug 658826 we disabled optimization in the D3D shader compiler to steer clear bugs.
Crash with up-to-date nightly: https://crash-stats.mozilla.com/report/index/bp-a4c522ef-2081-42c5-906f-19dde2111005
FWIW, it doesn't crash my 64-bit nightly build. about:memory's vsize is only ~650MB just before it crashes, so I don't think this crash is being caused by address space exhaustion.
The 64-bit Windows build reports similar framerates with and without media.ogg.enabled, so what you're seeing could be a Linux-specific issue. I'll test that platform soon.
Interesting. The upstream quake2 at http://code.google.com/p/quake2-gwt-port/ now works again in Firefox and I could reproduce the slowness with media.ogg enabled again on linux x86-64, firefox 10.0a1.