Hello!
Firefox browser v.66 (and many other versions) stuck in an infinite loop of CF checking.
And it lasts for a several months already. A few years before a same issue happaned but CF resolved it quickly.
Example:
Checking if the site connection is secure
www.gtxgaming.co.uk needs to review the security of your connection before proceeding.
Then it shows
Success icon Connection is secure Proceeding...
And it loops again and again.
In the same time old chromium browser does not expirience such problems.