Keyboard trap when using Firefox and Shift+Tab on some blocks

[afercia]

Looks like tabbing backwards when using Firefox breaks on some editor blocks. Seems to me it happens just for some block types, not sure if this is already a known issue.

To reproduce, just tab through the blocks and controls till the block that in the content sample content is after the split one ("... like this one, which is separate from the above and right aligned.") then tab backwards.
If the trap doesn't happen the first time, tab again forwards and backwards.

To make it simpler to understand, I've made a video using a very strong focus style:

https://cloudup.com/ckt5HyHe5K7

In the last part of the video, I'm just keeping Shift+Tab pressed and as you can see, as soon as the previous block toolbar appears, focus is moved back to the following block again, in an endless tab sequence loop.
I can't reproduce in Chrome.

[afercia]

I can't reproduce the keyboard trap in Firefox any longer.

However, I still see a different behavior between Chrome and Firefox.

• Chrome: tabbing backwards, it is possible to go through all the blocks and all their toolbars controls
• Firefox: tabbing backwards, on many blocks just the block gets focused and there's no way to go through the blocks toolbars controls

[afercia]

Although tabbing through blocks and focusing them is still inconsistent across browsers and block types, I can't reproduce the keyboard trap on current master. Closing.