Quite a lot. I mean, it's the same Gecko core, but there are a lot of pieces to Gecko. Mobile and B2G both use the same EGL backend for gfx, but they use diff

Quite a lot. I mean, it's the same Gecko core, but there are a lot of pieces to Gecko. Mobile and B2G both use the same EGL backend for gfx, but they use different widgets and some different optimizations (e.g. we know that we have permissions for gralloc on B2G, so we don't use a tiled backend). Desktop and Mobile/B2G share the layout, JS, etc but you've got all sorts of different gfx backends that could be used. Same code, just a lot of divergent pathways.