In version 2.7.8 I can drag and drop a repository to open it:
- on to the application folder icon
- on to the dock icon
- on to the application switcher icon
In version 3.0.0(200) no drag and drop methods work
NB - In the bug reporter I have selected the most recent version3.0b5 - but the 'about sourcetree' version is 3.0.0(200), which is not selectable here.