User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0

Steps to reproduce:

https://codepen.io/SaschaNaz/pen/bzWwNN

a {
	padding: 0 1px 0;
	margin: 0 -1px 0;
}
cite {
	display: inline-block;
}

<cite><a>FILE-API</a></cite>

Actual results:

Firefox shows:

FILE-
API

Expected results:

It should show FILE-API as-is as Chrome and Edge do.

Regression window:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=beca679d682be56233f8ad362ebcf190626be20d&tochange=413a21e421dbeb4be715a5cd28967719ba5bd886

Triggered by: e980c683af8c Jonathan Kew — Bug 809020 - Use a shorter "conservative breaking" range at word edges when dealing with letters rather than punctuation etc., and adjust existing tests accordingly. r=masayuki

(In reply to Alice0775 White from comment #1)

Regression window:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=beca679d682be56233f8ad362ebcf190626be20d&tochange=413a21e421dbeb4be715a5cd28967719ba5bd886

Triggered by: e980c683af8c Jonathan Kew — Bug 809020 - Use a shorter "conservative breaking" range at word edges when dealing with letters rather than punctuation etc., and adjust existing tests accordingly. r=masayuki

This isn't really a regression from bug 809020. Before that bug landed, we wouldn't break at a hyphen within 6 characters of the word edge, so that's why the FILE-API example here didn't show the issue; but if you try a longer example such as FILESYSTEM-INTERFACE, the issue occurs with earlier releases as well.

I don't think this is anything to do with hyphenation, the same issue occurs using regular text with spaces. This is the same issue as bug 1476925.

I guess this is a duplicate then.