I've not been able to use Paypal on Firefox+Linux, on and off for years now. The pop-up appears where it would ask you to log in and then normally you log in and either get "something went wrong" or it works. Now, it just immediately goes to "please try again later", before asking for who I am. This has been an issue on and off for so long, it's just the normal state for Paypal to be in for me. We're currently in a "not working" spell. It'll pass. Or not. It's paypal..
Frankly I don't mind the incentive to not use Paypal; gives me a good reason to tell business owners to support giving them the money directly (not through paypal or visa or whatever, just offer pre-paying via normal bank transfer) if they want my custom