I did some testing.
The problem seems to be that the login page is of type XHTML. If I download the page and load it locally with an .xhtml extension, pwm isn't seeing any fields, but if I rename it to .html, then it works.
So we can mark this bug as XHTML bug.
But I don't have any suggestion for fixing the bug or a workaround. Is there any setting in firefox to disable xhtml, so an xhtml page is treated like a html page? That might work.
And does anyone know of any xhtml login page that works with PasswordMaker?