Xeonist, I missed the libjpeg issues somehow. Maybe my build died before it got there. I tried again with the system-jpeg use flag in hopes of avoiding that problem and maybe picking up some recent fixes. The build still fails, but libjpeg doesn't kill it, so I don't know if the flag solves anything.
It didn't occur to me to look for armv7 in the log, or that gcc built for an armv6 target would be happy to make armv7 code. Silly me. Firefox's copy of libtheora is being built with -march=armv7-a -mfpu=neon, so that won't work. It doesn't get far enough for that to cause an error.
For me, it sill fails looking for libaecm_neon.a. I have confirmed that the build never attempts to make libaecm for armv7 with neon; it just later assumes its existence. I'm not sure this webrtc thing that uses libaecm is even a feature that I want.
In better news, Firefox 17 ESR now builds without trouble for me, so I can at least get security fixes. Looks like most of the newer Firefox build issues are from bad assumptions in new features, so hopefully 17 ESR will continue to build.