If you are using gmail, you probably could use "Check email from other accounts:" under "Settings / Accounts and Import". It fetches new mails periodically using POP3 or IMAP.
What I'm struggling with is consistency across pages, especially if you are not using a component framework.
I'll often end up with 50 similar, but different looking buttons.
On the other side when using a component framework, re-implementing all components when there are solutions already available (i.e. very similar in terms of look and feel Ant [1] or even Material-Ui [2]) sounds counter-productive.
Didn't you stumble upon such issue? How did you handle this?
It's not. But please make an issue on github[0] and if there's enough demand I will think about implementing this :)
Contributions are also welcome, though the codebase currently needs a bit of a refactor.
I am planning to add automatic tab sorting to the plugin. There's a github issue for this exact problem. I just didn't have time to implement this feature. ;)
With the first party isolate, mechanisms such as oAuth would not work. So the containers are less restrictive, but still allow you to have two sites with the same cookie context.
Shameless plug.
I made the ContainerTabsSidebar firefox addon[0], which is inspired by the TST. It groups tabs based on firefox privacy containers, which means every container has an isolated cookie store. I'm a tab hoarder and developed it to work for such "use-case".
It's very similar to the groups presented, but displays tabs vertically.
If you want to talk the email is in my profile.