FE is overeager when capturing keystrokes on FF

[dvdplm]

To reproduce do this:

1. Open telemetry.polkadot.io
2. Open a second tab in your browser
3. Close the new tab with the keyboard shortcut, e.g. Cmd+w on macOS
4. Notice the quicksearch bar in telemetry tab has appeared containing the letter w

Tested on Firefox nightly. On Chrome it seems to work as expected.

[maciejhirsz]

Seems fine for me on FF 92 (latest stable channel I have available).

[dvdplm]

It comes and goes, I can still repeat it here, v94.0a1 (2021-09-24). It seems important that the focus is not in the search bar in the second tab.

[dvdplm]

[CYBAI]

I can consistently reproduce this issue by following steps:

1. Press any keys to open the search bar in second tab with telemetry.polkadot.io
2. Close the second tab by cmd + w

I'm on Firefox 93.0 (64-bit) with macOS 11.3.1.