Sorry to hear about this problem. Does the page then have a second line with a reference number? That is characteristic of a website's perimeter security system (Web Application Firewall) blocking a suspicious connection. It can be caused by your IP address being associated with attack traffic, or something unusual about your request.

If you are using a VPN or proxy to connect, that is the first thing to check. For a VPN, it usually is clearly under your control to enable/disable. For a proxy, try this change:

Open the Settings page using either:

• "3-bar" menu button (or Tools menu) > Settings (previously "Options")
• type or paste about:preferences into the address bar and press Enter/Return to load it

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

Select "No proxy" then click the OK button at the bottom to save the change.

Any improvement?

Another user posted about this site again today. A thread back in 2020 mentioned needing to turn off ad blocking on the site: https://support.mozilla.org/questions/1294162