Thanks! Unfortunately I think that is impossible, because events are triggered after the tab is opened, ie the control on the tabs only occurs after.

I believe that this is so to avoid problem like sending POST requisitions, that it would be impossible to do a check if there were the use of `form method="POST" target="_blank"`, this is how the internal API of firefox (WebExtension: https://developer.mozilla.org/en-US/Add-ons/WebExtensions) and other browsers works.