From Bug 1749666:

(In reply to Henrik Skupin (:whimboo) [⌚️UTC+1] from comment #0)

Since bug 1745267 has been landed for Firefox 97 there is the new event TabSwitched available on the tabbrowser. This is more reliable as TabSelect which returns earlier - means before the tab switch actually happened.

We should update browser.js to make use of it.

When trying to implement this, we faced race conditions on Windows platforms between focusWindow and selectTab at https://searchfox.org/mozilla-central/rev/ecd91b104714a8b2584a4c03175be50ccb3a7c67/remote/cdp/domains/parent/Target.jsm#125-126 (see https://phabricator.services.mozilla.com/D139060#4740379)

This race condition only happens when using the TabSwitched event, so we decided to keep TabSelect for the time being.

This bug is about investigating the race conditions linked to the TabSwitched event and ultimately decide whether we should use it instead of TabSelect or not.