Re: [csswg-drafts] [css-align-3] the `safe flex-start` fallback alignment for `justify-content:space-between` is actually unsafe (#11937)

(+CC @tabatkins @fantasai as css-align-3 editors)

I'm adding a WPT to test this, marked as `.tentative` for now (pending a resolution to this issue), which will be at `css/css-flexbox/justify-content_space-between-003.tentative.html` once my [patch](https://phabricator.services.mozilla.com/D241670) lands and is merged.

That WPT is also available for live testing here:
https://bugzilla.mozilla.org/attachment.cgi?id=9472184

It shows a green square in all browsers, except in Firefox 136 (current release) through Firefox Nightly 138 where it's red.  (Though probably/hopefully we'll have a patched version out on all release channels in a few days, including a 136 dot-release, which will make it green again.)

I believe the spec requires browsers to show a red square (i.e. aligning the `start` edge of the flex item with the `start` edge of the flex container), but it seems that requirement doesn't match reality and isn't web-compatible, since it causes breakage in various web-chat platforms as reported in https://bugzilla.mozilla.org/show_bug.cgi?id=1953102 .

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Received on Friday, 14 March 2025 19:13:05 UTC