It would be nice to fire onload as soon as all script-observable effects are ready. In particular, we generally don't need to flush layout, only style. By avoiding a layout flush, we can save time overall if the onload script causes DOM/style changes. The one case that requires flushing layout is if there are web fonts that we *might* have to load depending on the text. We should be able to detect that case cheaply and only flush layout before onload in that case. Pre-requisites: * Make nsStyleSet say whether there are any font-face rules (should be easy) * Fix talos (?)

I'd really like to land this as soon after b2 as possible so it can bake...

Comment on attachment 456500 [details] [diff] [review] Like so Getting to this point means that we've already parsed all the style sheets? (We don't need to flush anything in order to ensure that?) If so, r=dbaron.

> Getting to this point means that we've already parsed all the style sheets? Yes.

Pushed http://hg.mozilla.org/mozilla-central/rev/a2c9de706e86 Then pushed http://hg.mozilla.org/mozilla-central/rev/3687d3cf3176 to bump assertion counts on one test that ended up asserting more of the same things it was already asserting.