This is it! xulrunner now builds and successfully runs the checks and xpcshell-tests on all release architectures, including arm, mips, powerpc and sparc, that were all failing 2 weeks ago. 2 patch pulled from upstream, 5 patches written and sent upstream, and several more as not quite successful attempts.
What puzzles me is that e.g. the arm issue in the test suite has been known upstream for a year, yet Firefox was released on maemo (arm) without it being fixed. I mean, it only took me a few hours (if you don’t count the time lost waiting for the builds to end), starting with no specific knowledge of arm, and even less of jit compilers.
Anyways, this all means work on 1.9.2 can go on.