Developer reply by Infocatcher
Rated 5 out of 5 stars
no longer working on v.51 beta.
This review is for a previous version of the add-on (0.2.0).See https://github.com/Infocatcher/Private_Tab/issues/237
and https://bugzilla.mozilla.org/show_bug.cgi?id=1318388
The Firefox itself should be updated... :(
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