The current version of Firefox 55 broke uBlock Origin. To get it working again, install the version of uBlock from the development channel. Scroll down the bottom of this page and select the development channel button.
This gets it working again instantly. This is the thing with free software, it gets a lot of updates, and this can be a problem, but it is very good to have free software options instead of closed source software that does not respect your freedom at all. Firefox is a very good web browser and well worth using for the sync function.
Direct link for the development version of the uBlock Origin browser.
An easy fix for an annoying problem.