Hi Hans, I've seen six similar reports today so far. One user reported that their ad blocker was hiding the contacts, perhaps due to a layout change by Yahoo. Could you:

Double-check Content Blockers

Firefox's Tracking Protection feature, and extensions that counter ads and tracking, may break websites that embed third party content (meaning, from a secondary server).

(A) The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

(B) Extensions such as Adblock Plus, Blur, Disconnect, DuckDuckGo Privacy Essentials, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix usually provide a toolbar button to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you sometimes need to click the button to see what's going on and test whether you need to make an exception for this site.

Was the problem caused by one of those?

Thank you so much

The ad blockers caused the problem. After disabling these the contacts were visible. Then I enabled the ad blockers again and the contacts didn't disappear. The problem is solved

Hans