I have tried them but it wasn't simple to use multiple profiles at once, nor was it obvious which profile you were using. I felt as though Firefox was discouraging their use. Are you using them?

Here is an article that talks through the steps (on windows but it's similar for others) https://www.howtogeek.com/209320/how-to-set-up-and-use-multi...

I use profiles because I need to test stuff with different extensions.

Before the Quantum release we had a pretty cool extension for managing profiles that is no longer available, sadly:

https://web.archive.org/web/20181102210053/https://addons.mo...

I hope it gets implemented again.

I now do the "about:profiles" thing I mentioned. I don't know why they aren't exposing Profiles in the UI in an intuitive manner, makes no sense. For my day to day use, I think Multi-Account Containers are better though.