The best place to report this is here:

https://webcompat.com/

Since it's a site specific problem.

Access Denied You don't have permission to access "http://id.digitecgalaxus.ch/login?" on this server. Reference #18.1c161502.1604645283.d0f52e4

This is characteristic of a web application firewall that deems your request suspicious. Since you can access from the same network using another browser, it probably is not IP address related. It might be caused by blocking certain headers, cookies, or scripts. However, I have no idea how to decode the message to determine more precisely what they don't like about the request.

You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be cautious. If you have a password or other data for that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data for that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox