Cross compile Firefox

Hi guys. Ideally I would like to be able to cross compile Firefox (and gecko driver) for raspberry pi (armv7) architecture from an Amd x86_64 architecture running Ubuntu, we have debootstrap installed so can run an emulated kernel in 32 bit mode to make things easier. We've got it compiling but getting stuck on the stylo library compilation (part of the rust code) and despite someone on a forum suggesting it the switch to --ignore-stylo (in the mozconfig) it says it's unrecognised.

If anyone has a mozconfig file they could share we'd be eternally grateful, and any other tips would also be most appreciated.