Thanks to the developers for this great addon! It really works!
The latest release of uBlock Origin 1.18.17rc5 was installed and works fine for me [FF 56.0.2 x64].
But when trying to install previous versions, the message "This add-on could not be installed because it was not verified" or "This add-on could not be installed because it corrupted" appeared.
uBlock Origin 1.18.17rc5: https://github.com/gorhill/uBlock/releases/download/1.18.17rc5/uBlock0_1.18.17rc5.firefox.signed.xpi
Please correct your negative add-on rating that was caused by a known FF developers problem...