Cannot use <tab> to go from Tags' input field to its Add button

[Daedalon]

In the edit post page under wp-admin there's the Tags widget with an input textfield, a submit button and a "Choose from the most used tags" textlink, in that particular order in both HTML and in the RTL reading order.

When the browser's focus is in the input textfield, as a user I expect that pressing the <tab> key moves the focus to the following item, the submit button, enabling the workflow of pressing <tab><space> to add a tag. In at least IE8 and any versions of Pale Moon / Firefox I've tried so far this isn't possible: the focus is moved to the textlink instead.

The technical reason for this is that the submit button has 'tabindex="3"'. Removing that tabindex solves the issue on Pale Moon / Firefox, but not knowing the reasons it was originally added, a different approach might be better.

Summary of issues:

1. Fix the <tab> handling in the Tags widget in wp-admin edit post screen by either
   1.a. removing the 'tabindex="3"' from the submit button in the Tags wp-admin edit post widget,
   1.b. change the tabindex's value to be such that it works on the most used browsers, or
   1.c. fix the functionality in JavaScript.

[Daedalon]

This appears to be fixed in 3.5 and has thus affected only versions 3.4.2 and earlier.

[SergeyBiryukov]

Fixed in [21311]. Marking as a duplicate of #21340.