try to remove cache of that website and disable AdBlock extension

It isn't possible to remove the 'cache' for a particular website. You may have to contact the website if that's possible. Adding a website as 'trusted' has made no difference to one website I have attempted to visit.

You could try creating a separate profile for viewing that site and install no ad blocker in that profile. It is possible also that Enhanced Tracking Protection is causing a problem so you could try disabling that on the website (click the shield icon at the extreme left of the address bar and switch the ETP button off).

https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop