Ok, here's my updated/simplified request for a URL-Prefix field.
The primary advantage of this functionality will be twofold: first, managing passwords for multiple users on the same domain, and second, for working with sites that do not really need to have a specific account set up (will just use the 'Defaults').
New Option:
Add a new checkbox option under the 'Username' field:
[ ] Prompt for 'Username' modification
(see #6. below for description of how this impacts behavior)
Changes to 'Master Password Prompt' window:
1. If new checkbox Option above is checked, the 'Master Password Prompt' window should include the 'Username' field, in editable mode.
2. If the User has opted to save the Master Password, this would be the only thing being prompted for, and if there is anything in it, it should already be selected/highlighted with cursor focus, so that the user can either simply hit 'Enter' to accept the default 'Username', or just start typing to replace it with something else.
3. If the User has not opted to Save the Master Password, then the cursor focus should be the Master Password field, but if the 'Username' field is tabbed into, instead of the User hitting Enter after the Master Password is entered, cursor focus should move to the 'Username' field automatically selecting everything in the field so the User can simply hit Tab then start typing the Username he wants to use.
4. If/when Username auto-populate is implemented, it is the *final* Username that should be populated, not the pre-defined one.
5. Once the above functionality is completed, 'Using URL' should display uneditable in both the 'Advanced' and 'Basic' Options windows.