Improve accessibility of default link focus styles in Firefox

[adamwathan]

Firefox 89 introduced new focus styles for form controls that are a big improvement in terms of accessibility, but by default it doesn't carry those improvements over to links, which still have a very subtle dotted border.

All this does is replace this old legacy rule from normalize.css:

:-moz-focusring {
	outline: 1px dotted ButtonText;
}

...with this:

:-moz-focusring {
	outline: auto;
}

The Firefox team is considering just doing this by default, as you can read here:

https://bugzilla.mozilla.org/show_bug.cgi?id=1708244#c3

Before:

After:

Before on dark backgrounds:

After on dark backgrounds: