How Mozilla recognizes password forms

[Michael ODonnell]

I've rigged Mozilla to remember my passwords
for various accounts (which I believe to be
safe because it's supposedly encrypted under
protection of a Master password - anybody heard
otherwise?)  and it somehow manages to detect
most instances where I'm supplying a password
and offers to remember it for me and then enter
it automatically from then on.  Sometimes it
doesn't do this, though, so I'm wondering if
anybody knows what it is about a given WWW page
that triggers Mozilla's password-remembering
behavior, or if there's some way to force it...