Hmm, is there any pattern to the new URL? Is it associated with any of your add-ons?

Could you type or paste about:policies in the address bar and press Enter to load the About Policies page. Normally, the Active panel says "The Enterprise Policies service is inactive." Does yours say that or does it list any policies that override default Firefox settings/behaviors?

Thanks jscher2000, about:policies returned in active panel Policy Name DisableAppUpdate Policy Value True. That was the only item included. There was nothing about 'Enterprise Policies'. The URL inserted was to a retailer's web site for entering their home delivery service. Normally the screen waits until I enter the Master Password before anything appears, however the only way to stop the behavior is to return to settings and re-enter my own URL. Its holding so far so I'm hoping it lasts.