Warning: There are some web pages that do not allow browsers to record or fill in the log-in information.

But if you go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) you can try a Form Filling add-on. I found that the form-filler add-on I use is not affected.

Thanks Fred, but to be clear - this particular web site in the past DID allow autofill. It only stopped doing so when I cleared my cache and cookies, as part of a house-cleaning. I have also spoken to the administrators of that site, and they claim nothing has changed. So the problem must be my side.

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

The problem STARTED when I cleared my cache and cookies. Deleting cookies again made no difference. I have tried Safe Mode before. Made no difference. I tried the same website in Safari, and it auto-fills the logon details. The problem is something suppressing the master password dialogue in FF.

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

If I check the page code then I see that the form is submitted via JavaScript AJAX. I've seen similar cases where Firefox didn't offer to save the password where also AJAX was used. The form doesn't have an ID and also no submit URL, so it is not possible to submit the form manually to see if that triggers the Firefox Password Manager.

FredMcD said

I found that the form-filler add-on I use is not affected.

Firefox only shows the master password prompt when it needs to access the Password Manager. Once you enter the MP then you are logged in to the software security device and you no longer get a MP prompt. If you cancel a MP prompt then you are logged out and need to re-enter the MP.

You can view the current status via this page (either Log In button or Log Out button is enabled).

• Options/Preferences -> Privacy & Security
  Certificates -> Security Devices
  Select: Software Security Device

Yup, that looks like it did the trick, cor-el! So far so good. Thanks - I would never have found that on my own!

OK, left it overnight to check - back to square one, FF won't trigger the MP prompt.

You can always manually login to the Password Manager by filling the prompt in the MP dialog that opens if you access the passwords.

• Options/Preferences -> Privacy & Security: Forms & Passwords: "Saved Logins" -> "Show Passwords"

Not sure what you intend with that, cor-el. I know how to access the list, and have done so many times to check if the website in question is listed there. It is not listed. Nor do I get an opportunity to add that particular website because FF does not trigger the MP prompt to allow me to do so.