Access Denied You don't have permission to access [URL] on this server. Reference #18.347c1ab8.1649099921.100c1168

That style of message is characteristic of a Web Application Firewall used to shield busy sites from denial of service attacks, scraping by bots, and other suspicious traffic. Something about your connections from Firefox look abnormal. The difficult part is figuring out what is causing it.

Some factors could be:

(A) Banned IP address. This often is temporary and clears up after a few hours.

Since you are using a VPN: There probably are numerous users who chose the same exit node (remote server), and the sins of the one are attributed to all. You can try a different exit node (remote server) until the problem with your preferred node clears up.

Otherwise:

You can set Firefox to "No Proxy" and see whether that helps. Either:

• Windows: "3-bar" menu button (or Tools menu) > Settings (previously "Options")
• Mac: "3-bar" menu button (or Firefox menu) > Settings or Preferences
• Linux: "3-bar" menu button (or Edit menu) > Settings or Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type proxy and Firefox should filter to the "Settings" button, which you can click.

Near the top of the dialog select "No proxy" and then click "OK" at the bottom. Test in a new tab.

IP bans typically end after several hours, so if you were temporarily subject to an IP ban yesterday, it may have resolved by now.

(B) Corrupted cookies. You can clear one site's cookies this way:

While viewing a page on the site (error page should work if the site address is in the address bar), click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that.

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try loading the page in a new tab.

(C) Modified headers. Browsers send a number of headers with their requests including the user agent (version string), acceptable response types, and referring site. The user agent used with your question looks normal, so I would investigate the referring site. The internal settings are well hidden in about:config, so unless you have been in there (or installing user.js files from strangers), an add-on would be a more likely culprit.

It is possible that your firewall or other security software blocks or restricts Firefox without informing you, possibly after detecting changes (update) to the Firefox application. Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full, unrestricted, access for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/en-US/kb/server-not-found-connection-problem
• https://support.mozilla.org/en-US/kb/Firewalls
• https://support.mozilla.org/en-US/kb/fix-problems-connecting-websites-after-updating