We currently disable WebRender when the screen size is too large for some configurations. We should actually take all monitors into consideration when making this decision, not just the primary monitor.

Before this patch, we only considered the primary screen when deciding
whether or not WebRender should be enabled. This is problematic for
Intel users where we don't want to turn on WebRender for large screens;
several small monitors are just as bad as one large screens. Now we add
up the pixel count for all the monitors when making this decision.

https://hg.mozilla.org/mozilla-central/rev/7b50fcb49160

Is this needed on Beta for the Intel WebRender rollout? If so, Fx70 RC week is next week, so it'll need to be uplifted soon.

Comment on attachment 9093128 [details]
Bug 1581606 - Consider all screens when deciding to turn on WebRender.

Beta/Release Uplift Approval Request

• User impact if declined: May get WebRender when it may be too slow.
• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Makes users less likely to get WebRender, but only if they have multiple monitors with Intel graphics cards.
• String changes made/needed:

Comment on attachment 9093128 [details]
Bug 1581606 - Consider all screens when deciding to turn on WebRender.

Good idea. Let's uplift for beta 14.

https://hg.mozilla.org/releases/mozilla-beta/rev/59ef27e0a17a