Go to any site (eg weather). In hamburger menu (bottom right) select Add To Home Screen. Launch Firefox using that Home Screen icon.

Install Onetab

Create a cookie exception (to prevent deletion)
When accessing a site you’d (from address bar/^i) open permissions and specifically ALLOW cookies for that site.

What addons in use? Is "Studies" on?

See "Manage Exceptions" (Privacy in Settings).
Typically, when accessing an "exception web page" you'd (from address bar/^i) open permissions and specifically ALLOW cookies for that site.