Access Denied
Sometimes the browser comes up with "Access Denied You don't have permission to access www.kroger.com" is the latest example. Once that message comes up nothing I do will get me to the website I want. I have to switch over to Microsoft Edge to continue my browsing.
Alla svar (1)
"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. 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. I've also seen cases where having "Resist Fingerprinting" enabled caused this issue to occur.
If this all doesn't work then you can try "Forget About This Site" in the right-click context menu of an history item.