https://tbpl.mozilla.org/?tree=Try&rev=6e653188b604 So the interestingly crazy thing here is that some of them we don't use at all (like FFLAGS), but some we do: CFLAGS, CXXFLAGS, LDFLAGS, LIBS BUT for the first three, we actually reset them in config.mk, with the value of OS_*. And guess what, OS_* is actually set to * in configure. (OS_CFLAGS=$CFLAGS, etc.). So for LIBS, which we don't reset in config.mk, we have redundancy between LIBS and OS_LIBS, which are both on the linker command lines... but sometimes we reset OS_LIBS with other values, so what's in LIBS is kept there, and what's in OS_LIBS is replaced. This patch takes care of all instances of OS_LIBS being replaced by appending to it instead, and removes CFLAGS, CXXFLAGS, LDFLAGS, LIBS and a few more from autoconf.mk. Those variables can still however, be adjusted in backend.mk and Makefile, and still affect the linkage commands.