Yahoo calendar temporarily not available doesn't seem like a browser issue. I have no issue setting up an appointment with you. ;-)) see screenshots Did you try with Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf Did you clear your browser cache? https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox What OS? What version of Firefox?