Meanwhile, I still don't have a good understanding of what's wrong with Amazon Music (still works great in 38.10), nor the issue with some users being unable to make changes to their default search engine stick. This is the problem with a single developer, folks: what I can't replicate I can't repair. I have a couple other theories in that thread for people to respond to.
Next up will be actually ripping some code out for a change. I'm planning to completely eviscerate telemetry support since we have no infrastructure to manage it and it's wasted code, as well as retina Mac support, since no retina Mac can run 10.6. I don't anticipate these being major speed boosts but they'll help and they'll make the browser smaller. Since we don't have to maintain good compatibility with Mozilla source code anymore I have some additional freedom to do bigger surgeries like these. I'll also make a first cut at the non-volatile portion of IonPower-NVLE by making floating point registers in play non-volatile (except for the volatiles like f1 that the ABI requires to be live also); again, not a big boost, but it will definitely reduce stack pressure and should improve the performance of ABI-compliant calls. User agent switching and possibly some more AltiVec VP9 work are also on the table, but may not make 45.6.
The other thing that needs to be done is restoring our ability to do performance analysis because Shark and Sample on 10.4 freak out trying to resolve symbols from these much more recent gcc builds. The solution would seem to be a way to get program counter samples without resolving them, and then give that to a tool like addr2line or even gdb7 itself to do the symbol resolution instead, but I can't find a way to make either Shark or Sample not resolve symbols. Right now I'm disassembling /usr/bin/sample (since Apple apparently doesn't offer the source code for it) to see how it gets those samples and it seems to reference a mysterious NSSampler in the CHUD VM tools private framework. Magic Hat can dump the class but the trick is how to work with it and which selectors it will allow. More on that later.