Input accept attribute in Firefox

Question

According to MDN accept=[MIME type] is supported in Firefox. However, I tried the following to no avail:

Answer 1

This is a known Firefox bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=826185

Fortunately, it appears there is a patch for the issue that should be reviewed soon.

Answer 2

I think it's a bug or not yet fully implemented.