The assertion happens in 64bit debug build on linux whenever I load some bugzilla bug page.

Seems like this is a trunk-only problem. Can't reproduce on 1.9.2.

Running mochitests on 64bit debug build (linux) crashes because of assertion Assertion failed: !s0->isQuad() && !s1->isQuad() (/home/smaug/mozilla/mozilla_cvs/hg/src/js/src/nanojit/LIR.cpp:2475)

Running mochitest on 1.9.2 doesn't have problems. (Didn't try --chrome nor --browser-chrome)

I'm seeing the same assertion. It also appears to be responsible for two failures in the js trace-test suite: TEST-UNEXPECTED-FAIL | trace-test.py | /home/zack/src/mozilla/moz-central/js/src/trace-test/tests/basic/bug539553-3.js: Assertion failed: !s0->isQuad() && !s1->isQuad() (/home/zack/src/mozilla/moz-central/js/src/nanojit/LIR.cpp:2475) TEST-UNEXPECTED-FAIL | trace-test.py | /home/zack/src/mozilla/moz-central/js/src/trace-test/tests/basic/bug525028.js: Assertion failed: !s0->isQuad() && !s1->isQuad() (/home/zack/src/mozilla/moz-central/js/src/nanojit/LIR.cpp:2475) This is going to prevent me from getting anything done until it's fixed.

The isQuad assertion is bug 539965 (with fix).

Sorry, I did not see this bug. It's been fixed on tm and m-c.