Merge pull request #24585 from davidflanagan/bug1074262

Bug 1074262: workaround graphics bug with will-change:opacity r=dmarcos(cherry picked from commit dc6d78742a0b327dce7be99245244f66db6f8279)
Merge pull request #24586 from davidflanagan/bug1074262-master

Merge pull request #24585 from davidflanagan/bug1074262 r=dmarcos