Perfect add-on! Using it for years...
Also new webextension version is working fine (in FF57 beta)
Would be nice if one could disable showing standard tabs..but as on could read e.g. on https://news.ycombinator.com/item?id=15342379
new API doesn't allow it yet (workarrounds for this could be also found in link above).
Another point which would ad the "icing on the cake" would be a possibility to show number of open tabs in the addnewtab field below last tab. This would help to be reminded when it's time to close some...