Mozilla has two big, though probably survivable, changes for 35 and 36. For 35, Mozilla is updating libvpx, a change that historically tended to upset our custom AltiVec VP8 decoding and will undoubtedly need tweaking to reassemble the fragments. For 36, though, Mozilla is merging DOM and content together, a major seismic shift to unify two core portions of Gecko that have been separate components in the source code even going back to the antediluvian Netscape days. Ironically, this second larger change is the least likely to be problematic for us because it's almost all cross-platform code which we don't have many patches in, but it may invalidate some sections of code indirectly.
Either way, I think I'd like to start the process early on these in order to have extra time for the expected additional merge work, so 34 is going to be changesets-only too; I'll do a little more fiddling with it and then upload them this weekend. I may release 35 as an aurora since that will necessarily require opt builds to be done, though I want to start on the port of MIPS-IonMonkey as soon as I'm done with 35 or 36.