Hi there, this is unlikely due to Firefox, but let's make sure we take out that possibility. Is there a specific website you are not able to pay, or many? Could you add which websites you have issues with? What is the error you are getting? And are you able to pay with your credit card in other browsers? (Chrome, Safari)

Hello Konstantina,

Thanks for getting in touch. Since I sent in my comment, I may be getting closer to figuring out the problem. My issue is with repairclinic.com and other sites that sell Whirlpool appliance parts. I finally heard back from one of their customer service representatives and they said that their websites are more strict than any/most other sites. The error report says that the address for my credit card doesn't match the shipping address I'm using, which isn't true. Other browsers come up with the same error, and I get it on my laptop as well as my cellphone. The customer service person said that I have to try with another card. It seems that these websites are the problem, so I'm just stuck unless another card works (though I don't have another credit card). I'll figure out something!

Thanks again for replying!