Add workaround for button outline problem in FF 78+

[flack]

Add a workaround for a problem where the close button outline is wrong in Firefox > 77

fixes #2003

[linux-foundation-easycla]

• ❌ - flack The commit (01e5462) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[flack]

I clicked through a couple of pages of this CLA stuff, but honestly all this legal crap is a bit too annoying for me. So I hereby grant anyone interested permission to re-submit this patch under their own name. If no one is interested, this PR can be closed

[fnagel]

@brianwarner Can you help out here with the CLA stuff? Thanks!

[brianwarner]

Thanks for your contribution, @flack. I see it's a one-liner, but unfortunately under the IP policy we can't really do much without a signed CLA.

[flack]

Good news, it looks like this is getting fixed in Firefox instead: https://hg.mozilla.org/mozilla-central/rev/1b335acf7f13