If message "Download failed. Please check your connection" appears, try to update Firefox. Go to "Help" -> "About Firefox". Update to ver. 66.0.4 and restart Firefox.
Your addons can be enabled now. Works fine for me.

Thank you!

This is the best of its kind. Thank you @gorhill

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...

Corregido el error de archivo corrupto, muchas gracias.-

Πολύ αξιόπιστο εργαλείο

Отличное расширение! Но дурацкий firefox перестал его поддерживать, поэтому надо искать какую-то альтернативу броузеру :(

The last firefox update resolve the problem!
I ve one word! 5/5!

(Last message, 1/5:
Not supported by firefox 57
This is a great Pub Blocker but it didn't works now!
Please upgrade it for firefox 57! and i ll change my ratting to 5/5 ! )

After 66.0.4(2019.05.05), FF fixed bug about using adblock. Now it is working well