Does this fault still occur with recent Firefox versions.
This seems to be a long-standing error. For me it started to happen some time in 2009, I think (always latest Firefox, under 32-bit Windows XP), and continues. I haven't done systematic elimination debugging. Several discussions can be found with a Google search; this is a common problem. When going to a website with a login name and password for which several name/password combinations have been saved, normally a dropdown list of names appears in the name box. Sometimes it doesn't, no names are offered. I have seen this attributed to Google Toolbar's autofill; I use the Google Toolbar, but disabling autofill didn't help; didn't uninstall the Toolbar to test. After starting Firefox the dropdown list appears, and stays consistently for a time; at some moment it stops working, and will then remain consistently absent until Firefox is closed down and restarted. On entering a name, the password is always found correctly. The problem occurs on other text boxes which normally remember a history (not just name with password), for example email address, cc, subject, etc. in a webmail page. This may only happen when there is more than a single stored value, i.e. a list, I'm not sure.