For awhile now I have trouble completing purchases on some websites when using Firefox. I need to open another browser like Edge to complete the transaction. Anything using "Shop with Visa" doesn't work and, for example, I just had to buy tickets on StubHub through a regular credit card submission. I bought them 4 times, got confirmation, and then had the order cancelled because it didn't go through. I called my credit card and was on with StubHub tech support. The final solution was to open Edge and make the purchase and it went through and I had the tickets a minute later. This is a big blocker and if its not resolved will have me exploring other browsers.
