I spent an hour with Microsoft support who told me this is a browser problem so I'm here. Firefox is my only browser, Yahoo is my only mail client: I'm up to date with firefox, always.

I have 2 desktops and 1 laptop. I bought the laptop with windows 10, use firefox and chrome and my 2 yahoo mail accounts no problem on the laptop, until a recent windows 10 update. Now I have no contacts and I can't manually insert contacts, it won't save them. I have 2 desktops both windows 7. I upgraded one in January. I don't normally use that computer so I was unaware of any yahoo mail issues. Desktop 2 is using version 18363.1016 while both the laptop and desktop 1 are on 19041.450. I finally gave in and upgraded my daily use computer to windows 10 yesterday 9/3/20. I now have no Yahoo contacts and it won't let me manually input them, it won't save them. So, Yahoo mail is affected on all 3 computers. I checked desktop 2 and there were no contacts there either. I called Microsoft support today, they did all kinds of things...I don't want to use the mail app, I want to use Yahoo mail. Oddly when I switched over to desktop 2 suddenly the contacts were there and everything worked fine . Nothing had been done to that computer...it is configured exactly like the computer I use daily. The laptop and the desktop still do not have Yahoo contacts are are able to save contacts. No clue how I got them on desktop 2, no clue how to get them on laptop and desktop 1. HELP. Thanks