Have you tried "Private Mode window" to see what happens? And what screenshot error are you getting so other registered users can replicate the error?

"You don't have permission to access..." errors are characteristic of a firewall that protects the server against misuse and this firewall thinks something is suspicious about the HTTP request. If you use a proxy or VPN then try to use a direct connection. Select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. *Settings -> General -> Network: Connection -> Settings You can try to clear the Cache and remove the Cookies for websites that cause problems via the padlock button or via "3-bar" Firefox menu button (Options/Preferences) to see if that fixes it. *https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can I've also seen cases where having "Resist Fingerprinting" enabled was causing this issue. *https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting If this all doesn't work then you can try "Forget About This Site" in the right-click context menu of an history item. *https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox