Yep, I think it's called "Containerise" with the British spelling. To make it work you need to remove your existing URL rules from the main container tabs add-on, or they'll fight like cat and dog if there's a conflict.

What's great about regex matching is that you can grab a regex for each of your Google accounts, and bookmark the URL that the regex matches. I've changed the Firefox search bar config to prioritise bookmarks in the results. I can now type 'gmail', and the top two results are:

Gmail (work)

Gmail (personal)

Each opens in opens in the correct container. The trick sometimes is finding a bookmarkable URL with a specific string that you can use in a regex.

To be honest it's one of the features I wish Firefox would add to their add-on because I don't like giving their party add-ons access to my data.