This is currently in Preview – planned to release very soon.
In the following weeks, Teams will be rolling out support on Safari 11+ on macOS. While in preview, there are known issues with Safari’s ITP mode and it is advised that users disable Safari’s Intelligent Tracking Prevention.Michael commented
Teams doesn't work in Safari and drag-and-drop for OneDrive and SharePoint isn't supported in FireFox. There isn't one browser I can use with Office365. Very frustrating.