The focused tab is not visibly focused in the tab strip if you focus it using the keyboard

[Softvision-CristinaBadescu]

[Affected versions]:

• Nightly 60.0a1
• Tab Split 0.1.9

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a clean Firefox profile with the latest Tab Split v0.1.9 installed.

[Steps to reproduce]:

1. Open Firefox browser with the profile from prerequisites and navigate to https://www.wikipedia.org/.
2. Click the "Tab Split" button from the toolbar.
3. Press "Tab" key at least 3 times and observe the behavior.

[Expected result]:

• The first tab from the tab strip is focused.
• The page's content has a colored frame.

[Actual result]:

• The other tab is visibly focused.
• The other page's content has a colored frame.

[Notes]:

• In order to focus the tab you need to click the tab from the tab strip or the page's content.
• Here is a screen recording with this issue: