No, so you don't seem to be able to have two different accounts open in two different browser sessions... I have multiple accounts open all the time, and you've got two options:

• Multiple browsers
• Multiple dapps

So, you could have one account open in Steemit, and another open in Steeve or Busy. I do that sometimes, but basically I find it easier personally to use different browsers... So Chrome is AussieNinja, Mozilla is Daclawboyz and Brave is NinjaVideo.

I haven't started using keychain yet... but I've been meaning to. Last I heard it wasn't ready for Mozilla yet, but I wouldn't be too worried about that..

Hope that helps!