Multi-window chat is in testing. I hope to have great news regarding rollout to the public rings soon.
We are working to ensure that multi-window and other future multi-window experiences are of the highest quality when they release.
Yes, Please prioritize this! The lack of windowed and tabbed chat is a huge blocker for my colleagues and I today. Teams needs the ability to support users who want to Meet, share and receive desktop share/streaming, and chat all simultaneously. It's what we do with Skype all the time and we really would like the improved reliability of teams along with it accommodating our work style with chat.
Screen sharing on Chrome and Chromium-based Edge is now supported. We also have released support for joining meetings from Safari, Firefox and IE browsers, with some limitations. For details, please see the following link: https://docs.microsoft.com/en-us/microsoftteams/limits-specifications-teams#browsers