Hi JaspreetSingh, I guess you want to use the Password Manager for some sites, but not others?

If you never want to use the Password Manager, you can disable it completely by unchecking "Remember logins and passwords for websites" on the Options page, Privacy & Security section.

Firefox stores your choice about never saving a password for the site, but that information can be cleared if you use either of these features:

• Clear Recent History (from the History menu)
  • If you use this, make sure to expand the Details and remove the checkmark from Site Preferences

• Clear history when Firefox closes (on the Options page, Custom settings for history)
  • If you use this, make sure to click the Settings button and remove the checkmark from Site Preferences

It's possible that other software on your computer might remove Firefox data, for example, privacy and cleaning programs. Do you notice any other site-specific information removed, such as permission to show popup windows or set cookies or use Flash, or zoom levels?

Options > Privacy --> Forms & Passwords

The Exceptions button opens Exceptions - Saved Logins shows the sites for which you selected Never. If that list stays empty after using Never or if it is empty after restarting Firefox or after booting up your PC you may have an application installed that is "messing with" files in the Firefox Profile folder. Many reports here about applications like Ccleaner causing issues such as that.

As far as creating a new Profile goes, they don't last forever and IMO as user from almost "day one" (Aug 2002 with Phoenix 0.3) it is best to create a new Profile when there is a major version change, Like when Firefox 29 was released, when Firefox 48 was released (when unsigned add-ons weren't allowed any longer), and then with Firefox 57. (And before those - Firefox 2.0, 3.0. and 4.0 which had major changes, too).

With the fairly new Reset / Refresh feature in Help > Troubleshooting Information, the process of creating a new Profile, while carrying forward your saved data - bookmarks, passwords, and other - makes that easy to do. https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox#w_accessing-the-troubleshooting-information-page = Give Firefox a tune-up - Refresh Firefox

Just let the process run its course - there is no "progress meter" - and the process may seem to get "hung" or be stuck as it can take 5 minutes to "do it thing". If you close it before completion of the process you will lose your data; I can attest to that - I did it twice to see what would happen when I closed Firefox before the Refresh process was complete. No Old Firefox Data folder on the Desktop and all my data was gone. But I did backup that Profile before playing with Refresh.

And IMO don't use the Refresh button on a KB support page; currently only the Default Profile as Firefox see's it can safely be Refreshed and the KB page with that Refresh button doesn't "screen" for whether the Default Profile is being used. I see that button with all my Profiles; I haven't tested that button in the KB article to see how refreshing a non-Default Profile works out. I do have limits on purposely leaving myself open to risking destruction of one of my well crafted Profiles - I'm not foolish. But I do push the limits to learn more about "new" features in Firefox, but with "throwaway Profiles" in my quest for knowledge.