This started happening with a number of users just this week

We need to figure which plugin is causing that.

Tools > Addons - Plugins - disable one Plugin and then restart Firefox to see if that solves it, try disabling them one by one and finding the culprit, then post here, please

Thank you

I havent added any Plugins for over a year. This problem just started in the last two days.

Type about:config in the URL bar and hit Enter.
If you see the warning, you can confirm that you want to access that page.

Pref = plugins.update.notifyUser if it shows as True, double-click that pref to toggle it to False

If that pref was already set to False, try disabling the QuickTime Plugin and then restart Firefox, to see if that is the culprit.