We need to disable Flash async drawing (bug 1340934) due to some recent Flash bugs (accelerated drawing bug 1359886, zero-sized Flash bug 1348629, and Xfinity video bug 1334803) that won't have fixes until Adobe's Flash 26 release on June 13. @ Jim, we had discussed only enabling async drawing for the 64-bit Funnelcake users, but shouldn't we leave async drawing enabled for all 64-bit users? 64-bit Flash without async drawing would break Stage3D and IME, right? Can you just enable async drawing with #ifdef _WIN64 so we don't need to flip the async drawing prefs in the 64-bit Funnelcake builds?

[Tracking Requested - why for this release]: We need to disable Flash async drawing (bug 1340934) due to some recent Flash bugs (accelerated drawing bug 1359886, zero-sized Flash bug 1348629, and Xfinity video bug 1334803). We won't have fixes until Adobe's Flash 26 release on June 13, the same day Firefox 54 will be released. So we should disable async drawing in 54 and try to ship it in 55.

Track 54+ as we will disable Flash async drawing in 54.

Tomcat backed out on Beta 54: https://hg.mozilla.org/releases/mozilla-beta/rev/6b0cf48f6481