Just signing in might not be enough to trigger it. When making a purchase using PayPal there has to be something to handle the transaction from and back to the merchants store. That would be the area possibly at risk, though as I said I made a purchase using PayPal late last night.

@ johnchisholm
Whilst I don’t use the Avast Online Security (AOS) add-on in firefox; johnchisholm try disabling the AOS add-on in your browser and see if that works - if not then try the just disabling the Web Shield.

You said avast is blocking, do you actually mean alerting on it (as some others are reporting alerts) ?