* It's way too easy to open new pages in the wrong container, and you can't convert an existing tab into another container. By the time you've opened a tab it's too late. Solution is to copy URL, create new tab, paste URL, which is a lot to do.
* There's no "New tab in same container" keyboard shortcut or button.
* If you click on a URL in a different app, or from the shell, you get a new tab in the default container.
* There's no way to designate an entire window or macOS space to a container. I have all my work stuff in a separate space, and no personal stuff should interfere. Similarly, if I'm already in a window full of, say, Google Cloud-related tabs, I don't want to clutter that window with containers.
The idea is great, but the implementation is nowhere close to being practical.
Chrome's profiles are too heavy-weight, but it has the right idea about the ability to couple window with profiles, because windows are "collections of tabs", and the most natural-feeling container of pages.
I have one Chrome profile for my personal apps, and one for work -- creating a new tab in one of the windows will automatically open it with the same context as the rest of the window. My experience with Firefox was that I'd have to manually choose which profile to open the tab in.
1. This required me to use my mouse (geh, maybe I could use keybindings to change this though? not quite sure how difficult that would be) 2. I'm not sure if this is just a me thing, but if I create a tab stemming from my 'personal' gmail account there's a pretty strong chance that it should also be a 'personal' tab. Maybe this is just a difference in how me and the Firefox team use tabs though?
Once I figure out how to get around those issues, (and when Streak's gmail extension works on Firefox...) that's when I'd be able to move over.
edit: apparently Firefox has had true instance profiles for ages! awesome. now I'm just waiting on Streak lol.