Here's my first guess: Firefox recently rolled out "Total Cookie Protection" to more users. This limits how sites can use "third party" or "cross-site" cookies, meaning cookies from different websites than the one you see in the address bar. Some sites pass you back and forth between different servers during login because they have their services spread out over a number of different servers -- not sure about AmEx. In those cases, you might be able to submit a form successfully on one page and then the next page says you are not logged in. Frustrating! You can make exceptions to this feature when needed (for each server that you visit as part of the process of using this company's services). More info in the following articles: * [[Introducing Total Cookie Protection in Standard Mode]] * [[Total Cookie Protection and website breakage FAQ]] Any difference?