Done mostly automatically via find/replace following the conversions
specified here:

https://groups.google.com/a/mozilla.org/g/firefox-dev/c/9sGpF1TNbLk/m/QpU3oTUuAgAJ

For the most part I think the "flex: N N" usage could be simplified to
just "flex: N", but I wanted to preserve behavior (-moz-box-flex sets
both flex-grow and flex-shrink).

I opted for explicitly setting flex-grow/shrink on the flex="" attribute
rules since you might want to override flex-basis regardless.

I changed legacy layout to also look at the order property rather than
-moz-box-ordinal-group because it made splitters and treecols easier (we
don't need to deal with both orders).

FYI, this is post-soft-freeze material, but TB would need to change a few styles. Most of it should be search and replace, see commit message. -moz-box-ordinal-group: 0 needs to become order: -1 because order and -moz-box-ordinal-group have different initial values (0 vs. 1 respectively).

Thanks!

Backed out for causing causing reftests and mochitests failures.

• Backout link
• Push with failures
• Failure Log mochitests
• Failure Log reftests
• Failure line mochitests: TEST-UNEXPECTED-FAIL | toolkit/content/tests/chrome/test_tooltip.xhtml | hover tooltip with long unbreakable text tooltip is wrapped
• Failure line reftests: REFTEST TEST-UNEXPECTED-FAIL | layout/reftests/box/flex-emulation-3.xhtml != layout/reftests/box/flex-emulation-3-notref.xhtml | image comparison, max difference: 0, number of differing pixels: 0

https://hg.mozilla.org/mozilla-central/rev/99aa47505e15

emilio, maybe worth backing out, given the various regressions?

The fixes are all one-liners, but still seems this should get a bit more bake time, so I'll prepare a patch to get it backed out of beta if that seems fine?

(Backing out also makes TB have to back out and re-land their fixes so that's also slightly annoying... In retrospect I didn't expect this amount of regressions and should've waited to after the merge probably...)

Dianna, fyi, I chatted with Ryan and he told me he'd be fine with backout-right-after-the-merge. Just fyi, I can prepare the patch right after the merge happens.

thats fine with me, ill keep an eye out for backout patch next week.

(As promised)

Thank you!

Backout from Beta v112: https://hg.mozilla.org/releases/mozilla-beta/rev/644d6d325eb6b7b8be313fc8d5cabbb0ee3cf623

push: https://treeherder.mozilla.org/jobs?repo=mozilla-beta&group_state=expanded&revision=644d6d325eb6b7b8be313fc8d5cabbb0ee3cf623

Comment on attachment 9322680 [details]
Backout of patch and follow-ups for beta.

Approved for 112.0b1

I don't know if you are aware of the possible very significant performance impact of your ongoing work?
We are seeing around 20% improvement in loading the style editor in the Browser Toolbox!
I imagine stylesheets are being displayed faster in the devtools UI thanks to modern flexbox being faster, or some change in styleeditor CSS which made it somehow faster.

== Change summary for alert #37603 (as of Thu, 09 Mar 2023 14:01:33 GMT) ==

Improvements:

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=37603