When accessing a website that would cause firefox to produce a sec_error_unknown_issuer error message, it is possible to view the certificate, accept it, and carry on anyway in the desktop version of firefox. In the mobile version, this option does not appear to be present If I view the certificate, there's an option to export it, but that's it. It's possible there's another button in the bottom right of the dialog, but I can't see it because scrolling is disabled.