Someone encountered some rendering problems after fx32 is released, and some issues are caused by OMTC, and some issues are related with GPU. Mozilla continuously fixed the related bugs until present.
After Fx34 is released, I noticed someone on Win7+ also has the strange issue, their part of about:support is
AzureCanvasBackend skia AzureContentBackend cairo AzureFallbackCanvasBackend cairo
And I think the normal value is
AzureCanvasBackend direct2d AzureContentBackend direct2d AzureFallbackCanvasBackend cairo
I asked someone for their GPU hardware, which is Intel HD Graphics 4400 / AMD Radeon HD 8670M Driver Dual GPU.
I searched the type in Mozilla Bugzilla, it seemed Fx33 changes limited the Dual GPU type, which will disable some features and they caused some issues, you can see in Bug 1097321. It is fixed in Fx37, and I try to ask someone who has the issue use the edition, which solved their problems.
Maybe the custom builders should consider the Bug 1097321 patch next edition.