I have FF Quantum 66.0.3, 64-bit.
I cannot install HTTPS Everywhere as of today.
The newest version of it is ( in my words, but based on the message ) "Not correctly Signed for inclusion as an extension for Firefox ( my version, or Firefox Quantum in general, I don't know ).
Another message also read "...because file ( or extension, I forget ) is corrupt..."
( I attempted to "save link as" :
The file is https_everywhere-2019.5.2.1-an+fx.xpi
Attempted to do "install extension from file" and again the "corrupt message".
( "Enhancer For YouTube" today is also experiencing the same sort of stoppage to it's update. )
( I do wonder if the issue may be on my side since no
one else has posted here with this problem ).
Please reply ASAP.