Created attachment 424380 [details] Screenshot Webpage: https://developer.mozilla.org/en-US/docs/Web/CSS/text-size-adjust Scroll down to the bottom of the page. Same problem happens on Chrome too. Left of screenshot is Firefox, right is Safari/Chrome.
Created attachment 424381 [details] testcase.html Here's a reduced testcase.
<rdar://problem/75894248>
I filed https://github.com/mdn/yari/issues/3373 and there is some activity there. It seems to be a difference in how browsers handle line-breaking after hyphens according to the last comment there.
Even more minimal testcase of differing behaviour from Jonathan Kew: data:text/html,<style>b{display:inline-block;width:1ch;}</style><b>-x-</b>
It doesn't not even need to be an inline-block element as this is simply about soft wrap opportunities and whether we consider the position after "-" as one. <style> div { width:1ch; } </style> <div>-should_this_be_on_the_second_line?</div>
I actually prefer the FF approach but don't have a strong preference on this -and I assume the spec is not clear on this case.