I did quite some work to have "--enable-altivec" work in ArcticFox. The FireFox AltiVec test did not work because it relies on GCC rejecting it if not supported by the CPU.
Most of the work was getting the 32bit AltiVec code actually work during a 64bit compile on a PPC970. But what about a non-AltiVec build? WIth some #ifdef's imported from TenFourFox... I was able to get it and produce, while compiling on a G4, a usable G3 optimized binary for Linux.
Result? A quite current browser for a 21 year old vintage computer! Fun! Not very fast and the beautiful tangerine clamshell has only 160MB of RAM, but still, one can browse Wikpedia!