Edit Project is an open sourced Visual Studio extension to add the context menu for editing project/solution file.
A known 'issue'
Because the Edit Selected Projects menu works for all kinds of projects, include .NETCore projects which have the VS built-in Edit Project menu. If you open a .NETCore project via this menu then open it via the VS built-in menu (or reverse), two edit windows will be opened.
If you have any question or problem, feel free to open an issue on GitHub.