You know I was really going to write this article for my reference because it was about the few lines to add the “Sign in as a different user” again rather than searching & copying it from other posts every time I need it but I then stopped & thought…

But why the hell they removed it!!! It’s killing the developers & administrators are suffering!!

The reason
is this option uses an unsupported browser feature which is unreliable and causes other issues. Currently this option does not work in IE 10 and Safari.

Ok I didn’t write the reason, I copied it from here because actually after adding it, it works!

Now I am signing in as a different user, who has a contribute permission,

As below, I am checking that the user logging name changed and also more sure that this user is contribute from the menu, it’s obvious; just checking the caching problem, I don’t see it happening at all.

Check this article to add the “Sign in as a different user”