I'd strongly suggest people create separate users in the browser, one for daily, one for Google, one for Facebook. This way in my regular browsing there's no Facebook or Google cookies reporting on what websites I visit. And with this new change, presumably in your daily profile, your browser remains signed out also. It's really easy and doesn't impact at all on workflow, if you want your Gmail you just click the use…
Firefox has a feature called "Containers", which is kind of this concept but with perhaps a better UX. https://support.mozilla.org/en-US/kb/containers
It might have been the fact that they were tabs in the same window, and it made it harder for me to control/organise/understand what was in what container.
Especially when opening new tabs.
I can't remember the details but I remember finding it fiddly. Maybe I'll give it another go.