I know Windows 10 is not yet public, but its now in evaluation copy form and releasing within 28 days.
First attempt to log in after opening a new tab is working as intended.
If the forum is open in a tab for a while, it seems like Edge gives me trouble signing in. When I open the sign in form and press username/password and log on, it kicks me back to the forum frontpage without being logged in.
Don't know if its EDGE issue or Xenforo - but would just make sure its out there.