Comment 86 for bug 1711337

 firefox_57.0.4 ubuntu xenial crash like firefox 58 ubuntu xenial , before it reach skia bug
=> 0xf4cd4790: strd r2, r3, [r1]
   0xf4cd4794: ldr.w r3, [r9, #4]
   0xf4cd4798: adds r3, #123 ; 0x7b
   0xf4cd479a: beq.w 0xf4cd4a34
   0xf4cd479e: ldr r1, [r6, #24]

 firefox_57.0.4 ubuntu trusty crash at skia bug
=> 0xf45d4b32: 20 f2 b1 11 ; <UNDEFINED> instruction: 0xf22011b1
   0xf45d4b36: 21 f2 b2 21 ; <UNDEFINED> instruction: 0xf22121b2
   0xf45d4b3a: 22 f2 b3 31 ; <UNDEFINED> instruction: 0xf22231b3
   0xf45d4b3e: 23 f2 13 ff bl 0xf47f8968

So firefox build with xenial toolchain have one more crash , mostly because of different build enviroment from trusty to xenial .

So a solution will be to build firefox with trusty toolchain .

About the cross compile set up , I was happy but to early , it compile fine for 30 minutes then stop compilation because a bug in rustc compiler .
I most used https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Build_Instructions/Cross-compiling_Mozilla and set up a xenial chroot . I installed some packages for xenial some for armhf . I uset rustup to install rust that can make target armhf .
But at one point I think it mix the include headers of x86 with the ones from arm .

I think the best is liek you said to set up a arm machine running ubuntu trusty and use that to compile all . I think that way will work . Using arm xenial just give one (or more ) crash not just the skia one .