Multiple Log Ins to one site w/ FF

I use different Log-Ins for a few web sites I visit. For instance at Express Scripts I need one to log in as myself and another to log in for the wife.

NS had a drop down that would allow me to choose from the two. Unless I'm missing something or have set up something wrong I don't see this feature.

 

Should allow it, but may require some extra steps.
First go to site both you and your wife log into and do a formal "Log off ".
Close the site, open the site, log on using your log on information.
Many sites offer a option to "Remember Me" to auto-log you in when you return to site ... be sure this option is NOT ticked. Once you are logged in, do a formal log off and close the site (I would also suggest closing/reloading Firefox). Again load the site and log on to site using your wife's log on information, making sure you do not tick "Remember Me ".
If the above does not work, you may have to go into Options|Privacy|Passwords| "View Saved passwords" and "remove" your saved log on information, then do above steps.