User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:81.0) Gecko/20100101 Firefox/81.0

Steps to reproduce:

This is in the latest stable version of Firefox 81.0 on macOS 10.15.6

Go to Firefox -> About Firefox and observe the visuals

Actual results:

1. The little circular progress indication during update check is not Retina-quality. It is noticeable low-resolution
2. There is a thin light line along the right edge of the "About" screen main content

See the attached screenshot

Expected results:

1. Circular progress should be high-resolution
2. No light line along the right edge of the content

One more thing - when the system preference is set to Dark mode, the "About Firefox" window still uses the light title bar.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

(In reply to Kirill Grouchnikov from comment #1)

One more thing - when the system preference is set to Dark mode, the "About Firefox" window still uses the light title bar.

This is covered by bug 1517182.

Not sure what the best component for this is, but it isn't widget:cocoa.

In an attempt to confirm the issue, I've taken several older issues.
As far as the attachment goes, can observe 79.0, 80.0, 81.0 and the initial attachment from the bug.

Any chance the low resolution - pixelation might be from the zoom-in over the image?
For my case that was what seemed to be at fault.

There is a thin light line along the right edge of the "About" screen main content

This issue appears to be limited to beta(82.0b8, 82.0b9)/RC as with nightly it's not visible.
In regards to it, filed bug 1670559 for separate tracking and debugging.

Kirill, do you still see this problem

Using developer edition 110, I do not see a white line.
I can't speak to the quality of the spinner.

So it turns out the code for selecting the throbber image is broken:

https://searchfox.org/mozilla-central/rev/d9dbf648b2f7557f6f06d27cce58546cc539cb2b/browser/base/content/aboutDialog.css#104-106

... doesn't work because it's an HTML image with the source hardcoded:

https://searchfox.org/mozilla-central/rev/d9dbf648b2f7557f6f06d27cce58546cc539cb2b/browser/components/preferences/main.inc.xhtml#516

Meh, this is rather trivial to fix....

We have no XUL throbbers anymore, so remove the html difference.

We could use <img srcset="..."> instead of image-set() in css, though
that'd mean a bit of duplication in about:preferences at least.

https://hg.mozilla.org/mozilla-central/rev/f66e0995f7a8