-moz-user-focus: none should force the element not to be focusable. The current behavior is hilarious:

• -moz-user-focus: none is the default.
• -moz-user-focus: ignore does something weird with events but otherwise behaves as none.
• -moz-user-focus: normal forces the XUL elements to be tabbable, but gets ignored on HTML otherwise.
• There are a bunch of other values that do nothing.

Proposal:

• -moz-user-focus: normal is the default.
• -moz-user-focus: none prevents focusability.
• -moz-user-focus: ignore should ideally be removed or aliased to none, but XUL uses it so might be tricky, we'll see.

Sounds reasonable to me, although it's used a lot in comm-central too.

(Oh, only overrides the tab index??)

(In reply to Emilio Cobos Álvarez (:emilio) from comment #0)

• -moz-user-focus: ignore should ideally be removed or aliased to none, but XUL uses it so might be tricky, we'll see.

In my understanding, none element is not focusable, but clicking it makes no element has focus. However, clicking ignore element does not make the focused element not blurred.
https://searchfox.org/mozilla-central/rev/648a427a0ffc4c62118dbb24bcd88a6b52f54d78/dom/events/EventStateManager.cpp#3522-3523

So, I think that it needs to be as-is.

(In reply to Masayuki Nakano [:masayuki] (he/him)(JST, +0900) from comment #1)

(Oh, only overrides the tab index??)

Right, and that's super-confusing.

In my understanding, none element is not focusable, but clicking it makes no element has focus. However, clicking ignore element does not make the focused element not blurred.
https://searchfox.org/mozilla-central/rev/648a427a0ffc4c62118dbb24bcd88a6b52f54d78/dom/events/EventStateManager.cpp#3522-3523

So, I think that it needs to be as-is.

Yeah I guess that the idea is that if you click on, e.g., a toolbar spacer, the urlbar isn't blurred? that's a bit weird compared to HTML, but sure, seems we need a hook for that, so fine to keep ignore.

If removing these were to become a compat issue in the wild, we could
alias them effortlessly. But honestly they're not even documented in MDN
so I'm pretty sure it should be safe to remove.

Make it be output-only, not having that confusing in-out tab-index
parameter that is special for XUL to become focusable with
-moz-user-focus: normal. Instead, do that explicitly in
nsIFrame::IsFocusable().

Also, call it IsFocusableWithoutStyle(), since that's what it is.

Depends on D195643

This is tested via the inert tests, effectively, but I can add more
explicit tests.

Remove rules that would otherwise change behavior (the other rules in
the tree apply to XUL elements and serve a purpose).

https://hg.mozilla.org/mozilla-central/rev/7182353bf85c

https://hg.mozilla.org/mozilla-central/rev/efcb1145c2cf
https://hg.mozilla.org/mozilla-central/rev/63ab69dfad15

https://hg.mozilla.org/mozilla-central/rev/d576a857df6f

Sheriffs, can we back out https://hg.mozilla.org/mozilla-central/rev/d576a857df6f from beta for now while we decide on a way to address bug 1871745?

Backed out d576a857df6f from Beta as requested: https://hg.mozilla.org/releases/mozilla-beta/rev/b746eaca3b44cb1c2649d868cc61b8d32dbcea85

Actually, it's still fixed in 123, backout was only for beta 122.

MDN docs for this can be tracked in https://github.com/mdn/content/issues/31928 - affected by answer to https://bugzilla.mozilla.org/show_bug.cgi?id=1871745#c13