Your instruction worked for Firefox. But from the three bar pull-down menu I had to select "Options" (the gear icon). Then the rest was the same.
Thanks for the idea of searching for "homemodel" because I went through this a few days ago and was faced with hundreds of cookies. I managed to find only one to do with HMEM (got tired of scrolling down the list). I deleted it and it did not help. I guess both is important.
Not sure about anyone else but re-loggin in was only a minor in-convenience. Once in the login dialog my username and password were already populated and I only had to press the "login" button. Maybe that was becasue I had only deleted one cookie?