I tracked down some intermittent failures in some paste-related tests to the fact that the tests are running early, when all style is "display: none" as part of our "FOUC-prevention". There's a simple fix.
Created attachment 5143 [details] use the more powerful flavor of updateLayout in cases that warrant it
So the vanilla updateLayout() will use display:none for an element whose style depends on a pending stylesheet?
Yes. See the code at the start of CSSStyleSelector::styleForElement.
Comment on attachment 5143 [details] use the more powerful flavor of updateLayout in cases that warrant it r=me