I haven't got much time to rewrite the whole block, and because I am not JavaScript or WebExtensions expert, I decided to concentrate on making the bug fix clear without additional refactoring.

The particular thing what is needed for refactoring is understanding the difference between lastFocusedWindow and currentWindow flags when querying for tabs. Chrome current window docs mention that currentWindow is where the code is currently executing. I understand that when I click extension button on the toolbar, the code is executed in the window with the toolbar. Then I don't understand why lastFocusedWindowis being used.