Tab hoarders unite! (I'm pretty sure that because of the multi-account component, this isn't what the original creators thought would be its use but hey, it works great for it as well)

I honestly love this extension, but I couldn't give it that last star. There's two or three things I would love to see updated for containers that would definitely earn that last star though: switching a tab to new containers from either no container or a different container (one at a time or en masse), as this would allow first time container users who hoard tabs to move them over a little more easily; the ability to shift around containers (i.e. move up a container that's in constant use up, or move one that I don't really care for down), as currently the only way to "move" them is by deleting the container and then making it again which puts it at the bottom of the list; and if you could make it so that tabs in a closed container (or open for that matter) would sync with firefox sync (and the containers themselves!). These changes are the only things getting in the way of this being from my perspective the ultimate tab sorter.

Containers has honestly helped me organize my online activity and helped me put my distractions into a side tab, though; so I honestly say this is one of, if not the, best add-on on Firefox, which is (in my incredibly biased and tab-hoarding opinion) the best internet browser.