Testing Firefox 3.5.7 on ARM with "valgrind --smc-check=all" highlights that system call 181 (sys_pwrite64) is not handled by Valgrind. This is non-critical in at least this instance; Firefox doesn't fall over because glibc then falls back to some other combination of system calls which Valgrind does handle.
*** This bug has been marked as a duplicate of bug 249996 ***