Bugzilla

Hello, 

I managed to encounter this crash signature with the following steps on macOS10.15.6:

1. Launch FF.
2. Go to https://en.wikipedia.org/wiki/Facebook
3. Toggle between Portrait/Landscape a few times until Print Preview is no longer loading.
4. Tab crashes. (in some instances it took around 1-2 minutes for the tab to crash)

Hello, 

I managed to encounter this crash signature with the following steps on macOS10.15.6:

1. Launch FF.
2. Go to https://en.wikipedia.org/wiki/Facebook
3. Toggle between Portrait/Landscape a few times until Print Preview is no longer loading.
4. Tab crashes. (in some instances it took around 1-2 minutes for the tab to crash)


Firefox 81.0a1 Crash Report [@ nsDeviceContext::UnregisterPageDoneCallback ]

This bug is for crash report bp-11c1aa2d-c833-469a-b930-b5bba0200813.

Top 10 frames of crashing thread:
```
0 XUL nsDeviceContext::UnregisterPageDoneCallback gfx/src/nsDeviceContext.cpp:713
1 XUL nsPrintJob::DonePrintingPages layout/printing/nsPrintJob.cpp:2519
2 XUL nsPrintJob::FinishPrintPreview layout/printing/nsPrintJob.cpp:2703
3 XUL nsPrintJob::MaybeResumePrintAfterResourcesLoaded layout/printing/nsPrintJob.cpp:1647
4 XUL {virtual override thunk} 
5 XUL nsDocLoader::DoFireOnStateChange uriloader/base/nsDocLoader.cpp:1331
6 XUL nsDocLoader::FireOnStateChange uriloader/base/nsDocLoader.cpp:1294
7 XUL nsDocLoader::doStopURLLoad uriloader/base/nsDocLoader.cpp:898
8 XUL nsDocLoader::OnStopRequest uriloader/base/nsDocLoader.cpp:622
9 XUL {virtual override thunk}