I'd like to suggest a fix for this bug.

This bug appeared with the fix of bug 447788 somewhere around version 3.5.

In bug 447788 the problem seems to be that when you register on a mediawiki Wiki site, you can register using a lowercase user name, "john" but the site then pre-fills the user name using an initial capital, "John".  The complain, if not mistaken, was that the password, even though it was saved, was not auto-filled.  The reason was that Firefox did not match username "John" with the saved username "john".

The fix was to make the whole password manager case insensitive.  Justin Dolke noted: "The main problem I was worried about was if doing this could cause interactions resulting in saving duplicate logins for "myname" and "Myname". But I don't think that's the case (and may even help avoid it)."  But since then there have been numerous complaints about Firefox forbidding logins with different cases.


So I'd like to suggest the following behavior for the case-sensitivity problem:


User name auto-fill
- FF has a method that identifies a password field and the associated username field.
- If the username is blank and FF has a single username/password saved for that web page, then the username and password should be auto-filled from the saved username.  That should happen when the page loads.
- In no circumstance should FF change the username that was pre-filled by the web site or entered by the user.

Password autofill
- If the username gets autofilled when the page loads, the password should be auto-filled at the same time.
- If the username was pre-filled by the web site, and the username matches a saved username/password, then the password should be auto-filled when the page loads.
- When leaving the username field, if the username field was changed and the username matches a saved username/password, then the password should be auto-filled with the saved password.
- Which username "matches" a saved username/password is described below.

Saved usernames/passwords
- A flag "case-insensitive" tells that a saved username/password entry also applies to all alternate cases for the username.
- A username that is marked case-insensitive cannot appear with a different case among saved usernames/passwords.

Matching usernames with saved usernames
- A saved username matches the exact same username or, if the flag is set, any username that is equal ignoring case.

Saving the password
- When a user submits a form:

  - If the web page is flagged never to save passwords, do nothing

  - If the username matches a saved username/password and the password matches, do nothing.

  - If there is no matching username saved for that web site, ask the usual question:
      "Remember password for user "xxx" on yyy?" with options "never", "not now" and "remember".
    Remember stores the username/password.  If another username exists, identical but with another case, then save it as case-insensitive, else save it as case-sensitive.

  - If there is a matching username/password and the username uses the same case as saved, but the password is different, ask the usual question:
      "Update saved password for user "xxx" on yyy?" with options "not now" and "update".
    Update replaces the password in the saved username/password entry.

  - If there is a matching username/password and the username uses a different case and a different password than saved ask:
      "Replace saved username and password for user "xxx" on yyy?" with options "not now", "replace" and "remember both (case insensitive)".
    Replace replaces the username and password in the saved username/password entry.
    Remember both (case insensitive)  creates a new entry and marks both entries as case-sensitive.
    Note: here, "xxx" is the saved username.

Password manager.
- The case-sensitive flag should be visible in the password manager.  It should be possible to set  it (make it case-insensitive) but only after deleting duplicates.
- There is no other way to revert to "case-insensitive", as it involves removing saved username/password entries.


Summary
The saving of passwords remains case-insensitive as long as no conflict occurs.  If the user uses different accounts with different cases, but still with the same password, then saving a single password with a case-insensitive username is still appropriate.  Only when trying to set a different password for a different username case will FF ask how to treat case-sensitivity.

One thing that is still missing is the possibility to change the case of a username that was saved wrongly.  The problem being that it will auto-fill with the wrong case.  For that, the last case ("replace?") should also be triggered when the user submits a form, and the username was auto-filled from the saved usernames, but the user changed the case manually.  I don't know if that logic can be implemented in a simple way.


Best regards,
Florian Fischer