Containers are enough for your use case. I know that for some usage cases, are enough. But for nearly 90% users, they are enough and even better that profiles.

You sure?

What I want to do is sandbox my accounts, specifically my work account. Here's a sceneario

I click a link in slack, I want the link to open in the work container.

How do I do this?

Because using containers, It will default open in the default container, i then have to right click the tab, and say "open in work container" .. which then opens that tab again, in the Work Container.

What I want is to not have to do that extra work. Click link -> Work Container.

You can't, at least, not default... you need to add extra plugins, like Multi-Account containers or whatever the plugin is called. That's a LOT of work for the average user. Compared to profiles where when you click the link, it opens in the last active window, which remembering windows are profiles, will be most likely the right profile. So if im working constantly on my work profile window, i click slack, and then click a link, its right back where i want.

The problem with container tabs, is that its tabs, not windows. So is there any way i can say to firefox "this new window is WORK Containers please"

Looks like there's an extension which adds a new protocol handler, which allows firing the container you like for a given link from the command line.

It's available at https://github.com/honsiorovskyi/open-url-in-container and Mozilla Extension store, so you can directly install it.

I think you can register a new "application" to open links, not set at default, and use Right Click -> Open With -> Firefox (WORK CONTAINER).

Will that work?