Firefox Screenshot outputs empty white image when privacy.resistFingerprinting is enabled

[Paivi-Harkonen]

Steps to reproduce:

1. Install Nightly.
2. Enable privacy.resistFingerpriting.
3. Go to https://www.mozilla.org/
4. Click on the drop down in the urlbar and choose screenshot.
5. Save your screenshot.

Actual results:

This outputed a white image due to the canvas being blocked by default.

Expected results:

This outputed shouldn't be a white image due to the canvas being blocked by default, maybe there should be a whitelist for the screenshot addon.

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https://bugzilla.mozilla.org/show_bug.cgi?id=1412418

[ianb]

I've opened Bug 1412961, which is about privacy.resistFingerprinting, since we can't fix this in Screenshots itself.

We could notify people about this bug, and I'll leave the bug open to discuss that option. I don't think we should disable Screenshots (the fingerprinting code is experimental, so IMHO we should let the bugs all hang out), but we could pop up a warning.

[ghost]

Thanks for filing that bug. We'll track this there.