RedditNotifier-WE by Druco

Updated version of RedditNotifier by Bradley Rosenfeld to work with Firefox Quantum.

Features
- Toolbar button to allow easy access to your reddit inbox.
- Notifications (can be turned off) when you have new messages or moderator mail.
- Watch your favorite subreddit for new posts.
- Plays a sound when there are new messages (can be turned off).
- A persistent bubble on the toolbar button that tells you exactly how many messages you have.
- Panel to quickly view and open unread messages and subreddits.
- Restartless; just install and you're ready to go!
- Doesn't store login credentials. Just log into reddit like you normally would.
- Customizable refresh time (10 seconds to infinity).

CAUTION:
This add-on DOES NOT work if the built-in Tracking Protection is enabled in Firefox (under Preferences->Privacy & Security). I don't know of any way around this so it is unlikely to be fixed in the future. It is known to work with Ghostery so add-ons that provide tracking protection may provide an alternative to the built in feature.