Deactivating the extension replaces the current tab content by a default new tab, destroying all data one is working on and even literally erasing the tab from tab history (no way to use Back). Activating the extension instead closes the current tab. Even now, the tab is completely lost in the void, because ctrl+shift+t causes a "new tab" be opened INSTEAD of the previously closed tab. (EDIT: The previously closed tab is only lost due to a hazard when I press ctrl+shift+t twice very fast.)

Other than that, the addon does what it has to do, and I appreciate the option to gain tab focus instead of the navigation bar. One last thing i'd find very useful is if typing into the address bar before anything gets loaded postponed the process of replacing address bar (deleting anything I've typed) and taking the focus away. Not sure if firefox even provides so much API to achieve this.

// Reply: Well the issue is critical and deserves at least an acknowledgement in the description, as it's an anti-feature. Honestly though, I haven't seen WebExtensions implementation, but I don't believe you at all. I can imagine several workarounds, neither of them were even considered. Is there no API whatsoever to access the last closed tab history, so that you can offer a way to manually re-open the lost tab? Is there absolutely no way not to process your addon when the user presses Ctrl+Shift+T? Is that specific event impossible be detected? Can you not let the default implementation (optionally) load first before redirecting to the user specified site? Also the issue could be reported to WebExtensions devs... Completely blocking the "re-open last tab" support is definitely not acceptable as a final decision. (But I know the WebExtensions suck, there are so many other addons that no longer work even in theory in the new Firefox.)

-> Okay so I decided to try to fix my issue myself and even though I found a WebExtensions solution, there was a bug that I couldn't fix. Still, some safety workarounds could be made. Luckily, I found a workaround instead: disabling the focus setting solved the issue, because it still focuses the new page anyway (the setting is broken), thus it works exactly as I wanted. The referenced issue is here: https://github.com/cadeyrn/newtaboverride/issues/167