I use Firefox (latest version) and have the Firefox Add-on installed.
After you have logged into a site for the first time, the alert to save passed is in focus and totally accessible. You can tab around: Save, Don’t Save, User Name and Password; and make your choice.
But if you navigate away from the alert, you will not get it back. Firefox has no hotkey for that. With the Firefox Add-on, you can press NVDA + Ctrl + N. It is supposed to read the last notification and takes the system focus to it if it is possible. But all you hear is: “Last alert about xx seconds (or minutes, whatever the case may be) ago. Couldn't capture the texts of the notification.” Other methods suggested by folks in this thread don’t seem to be able to salvage the alert, I am afraid.
So, if you have bypassed that alert, just wait for it to pop up after your next login.