Can't join skype meetings? Can't Open sharepoint links? Can't click any links? Chances are you've got something set as your default for .htm .html or .xhtml file types. In all cases I've come across (one recently and several years ago) it was firefox.
You need to go to edit the registry and search for the extension then delete the default.
In windows 10 once you have a default you can't set it back to nothing using the settings menu which is stupid but I guess it's to stop stupid people doing that by mistake.