Cannot Make Firefox As My Default Browser.

Every time I login on my computer, there is already an open Firefox webpage with a dialog box asking me if I want Firefox to be my primary default browser. Once I click "Set a Default Browse", a Microsoft Edge webpage appears giving me a list of choices of Microsoft application to select to be my browser. Firefox is not on the list. There is also a dialog box that appears on the lower right corner of the screen showing me the steps on how to make Firefox my default browser. The choices are "Show Me How" and "No Thanks". When I click the "Show me how", I am taken to Firefox setting, once I click the "Make Default" I am taken back to the list of Microsoft applications to choose as my browser. The bottom line is I cannot make Firefox my default browser anymore. In fact, I am not even sure if I am sending this message to Firefox or Mozilla. This is the URL that I see on this https://support.mozilla.org/en-US/questions/new/firefox/form. Would you please check and correct the problem. I cannot make Firefox my default browser. Would you check if Firefox is my default browser.