I had the same exact concern, and I haven't been able to find reliable confirmations on this being completely impossible either.

It's easily testable, though, that a webpage that isn't focused (because an extension's pane is open) doesn't receive input events. Likewise, Chrome [1] and Firefox [2] extensions themselves cannot bind to relevant keys for example. All in all I would say that going through an empty tab is unnecessary - even though I got into the habit of doing it as well - and even if this wasn't true 2FA should be enough to thwart most malicious actors.

[1]: https://developer.chrome.com/extensions/commands [2]: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...