In some cases Direct2D-accelerated drawing is slower than the non-accelerated path. Jeff Muizelaar fixed a severe gradient ‘hang’ in bug 823147.
Avi Halachmi diagnosed a significant menu performance issue in bug 832641, this was promptly fixed by Matt Woodrow.
Ehsan Akhgari fixed a chromehang caused by leftover debug code: bug 830765.
Justin Lebar fixed an issue where telemetry memory reporting code was accidentally triggering expensive ‘release memory to OS’ operations: bug 789975.
Sometimes Firefox takes a long time to shutdown. We also have a timer that regularly triggers cycle collection. Olli Pettay disabled this timer during shutdown in bug 822849.