I recently scheduled a consulting appointment with one of my regular customers whose Mac had started to display a “multi-hop cycle detected” error whenever she opened either Safari or Firefox. Acknowledging the fixes suggested on various websites, I was able to eliminate the screen error within minutes of my onsite visit.
My client uses the web interface to send and receive her Yahoo mail. A quick check of the Safari and Firefox Preferences windows revealed that the URL address set as her home page for both browsers was pointing to the inbox of her Yahoo mail account, but that this address was corrupted. I manually changed the Startup home page for both browsers to “http://mail.yahoo.com,” then closed both browsers. When I reopened Firefox, I immediately saw the inbox for her Yahoo mail account and the screen error had disappeared. When I relaunched Safari, my client was good-to-go after her assistant entered her mail password in the Yahoo dialog box.