XUL doesn't support the language attribute, so it should have no add-on impact.
No in-tree consumers use the language attribute to enable language extensions.
Created attachment 697450 [details] [diff] [review]
Get rid of the outparam, please.
Created attachment 697481 [details] [diff] [review]
Removed the useless outparam.
According to the comment, the language attribute already lost the ability in HTML.
> XUL doesn't support the language attribute
And it looks like it was wrong.
I've added this bug to the compatibility doc. Please correct the info if I'm wrong.
(In reply to Kohei Yoshino from comment #6)
> I've added this bug to the compatibility doc. Please correct the info if I'm
The language attribute in HTML used to ignore the JS version before this bug. This bug is just a cleanup for Web pages.
On the other hand, XUL language attribute has changed the behavior. Therefore, this is a add-on compatibility bug (not site compatibility).
Oh, Okay. Removed this bug from the document.