Well whatever the heck was going wrong for me before is all better now. This is significantly easier to use than the multi-container version, and doesn't stop you from using that one anymore for new, special containers. The way this one works is pretty nice, too - it "just works" out of the box, making it a good starting point for privacy novices (like me).

This is one of the biggest reasons I switched to Firefox.

I'd like to rate this higher, but it breaks some websites by preventing images from loading at all, especially if those images are embedded from Instagram. Took me forever to figure out why so many websites I normally use without issue were suddenly broken. I have this extension disabled for now, hopefully devs will fix this issue soon and I can start using it again.