I am also affected by this bug since 61beta releases installed from Debian repositories.
The problem is with system dictionaries as well as with those installed as addons. When activating spell checking the following error is printed to the console (here trying to use czech dictionary, but it is equivalent with all others): System dictionaries: error: file:///usr/lib/firefox/dictionaries/cs_CZ.aff: cannot open error: file:///usr/lib/firefox/dictionaries/cs_CZ.dic: cannot open error: file:///usr/lib/firefox/dictionaries/cs_CZ.aff: cannot open Dictionaries installed as an addon (profile directory substituted): error: file:///home/mister/.mozilla/firefox/[profileID]/extensions/cs@dictiona ries.addons.mozilla.org/dictionaries/cs.aff: cannot open error: file:///home/mister/.mozilla/firefox/[profileID]/extensions/cs@dictiona ries.addons.mozilla.org/dictionaries/cs.dic: cannot open error: file:///home/mister/.mozilla/firefox/[profileID]/extensions/cs@dictiona ries.addons.mozilla.org/dictionaries/cs.aff: cannot open There is an upstream bug report here: https://bugzilla.mozilla.org/show_bug.cgi?id=1469740 Regards, Jan Janský
