Works well, one small issue is that if you click a direct product link (non-smile) while not logged in, it goes into a redirect loop until you open a new tab, go to Amazon Smile, and login. Doing that then allows the tab to load.
Other than that, works very well! Thanks to the dev.
Works great for shopping, but unfortunately catches AWS websites as well as Amazon Commerce, so it breaks getting to console.aws.amazon.com. A feature to disable for *.aws.amazon.* would help greatly. I had to disable it.
Before today I would have said this was no longer working and hasn't been for some time. Today I removed the add-on, restarted and re-installed, and it started working. I'm happy again. I'm using Firefox 63.0.3.