I just upgraded and experienced the same issue. Since liberpoolesque
reported that Abrowser 72 works with a fresh install of Trisquel, I suspected
that there has been some non-backward-incompatible change Firefox making
older profiles files invalid. I ran
$ mv .mozilla/abrowser .mozilla/abrowser~
so that Abrowser would not be able to find my profile, after which Abrowser
started normally, creating a new default .mozilla/abrowser.
Unfortunately this loses all user bookmarks, history, settings, etc. It
should be possible to copy any important data from .mozilla/abrowser~ to
.mozilla/abrowser, but it would be preferable to know exactly what about the
older profiles is cause the issue so that we can just fix that. I'll look
into this more later today.
