Manually add username/password to Saved Password list?

If you're a developer with 3 minutes to spare, this is how to do it without installing another add-on.

1. On the login page, Inspect Element the username and password fields and take note of their name (or id, if no name is given) attributes. For example on Khan Academy, that would be identifier for the username and password for the password.

2. Inspect Element somewhere on the page. Find a small div or so, that's easiest.

3. Right click the element in your inspector and choose Edit As HTML.

4. Add the following HTML:

   <form method=post>
     <input name=identifier>
     <input type=password name=password>
     <input type=submit>
   </form>
   

   Replace the names (identifier and password) with the names from step #1. Note that you should not replace type=password, only the name=password field!

5. Enter your credentials on the page in this form and hit submit. Firefox will now prompt you to save the credentials. The website will probably burp up an error or ignore the request or something, but we don't care about that.

Why does this work? Some sites deliberately do something funny to prevent you saving the password (the browser's remember password feature is often seen as insecure); other sites just have a funny form mangled beyond recognition for Firefox. Adding this simple form makes Firefox detect it and when you enter your credentials, it will prompt you to save them.

Now on the login page, as long as the fields actually have name attributes at all I guess (and it probably needs to be wrapped in a <form> too, I don't know), Firefox will typically recognize the fields and be able to fill them for you.

Alternatively, it might simply be that the website has autocomplete=off set on the field. You can remove this as follows:

1. Launch "Tools > Web Developer > Inspector" and hover your cursor over the form
2. When the form element is highlighted, look for the attribute that says autocomplete='off' (You may have to scroll up and look for the form element in the Inspector tab)
3. Double click the attribute and change off to on
4. Firefox should now ask you to save your username and password

Since Firefox 70.0 this is now a built-in feature in the password manager (Firefox Lockwise). To access it navigate to the saved password list or type about:logins in the address bar; At the bottom left corner click the Create New Login.

PS: Solution to my specific problem - App Store Connect not saving my credentials - I put https://appleid.apple.com as the website address when adding a new login.

To simplify the advice by the top poster, the reason the feature doesn't work on some websites, whilst working on others, is due to the non-standard and/or malicious code used by enterprise websites like Hertz.com.

In the case of Hertz.com, I was able to make Firefox save the password by doing the Inspect Element on the Login button, and then doing the Edit As HTML trick, and changing the type of button from button to submit; without this trick, even the Remember Password bookmarklet wouldn't work:

    -<button type="button" class="primary gblFloatLeft" id="loginBtn">
    +<button type="submit" class="primary gblFloatLeft" id="loginBtn">
                                                Login 
                                            </button>

In short, doing Inspect Element and then Edit As HTML to fix all the malicious and non-compliant HTML works wonders!

I know this question is old, but I figured I'd throw in my solution anyway.

Since Firefox sometimes fights me on certain websites, the solution I've developed is using another browser such as Chrome and saving the username/password there. Then you can import the login information for the specific website from that other browser.

After you've saved the password in the other browser, you can do the import by following these steps:

1. Going to the website in question and clicking the "(!)" to the left of the URL in the address bar.
2. Then click the > button to "Show connection details".
3. Then click the "More Information" button at the bottom of this little dialogue.
4. In this new dialogue, go to the "Security" tab.
5. Click the "View Saved Password" button.
6. In this new dialogue, click the "Import" button, and follow the steps from there.*

*These steps are valid for Firefox version: 62.0.2. I imagine it's similar for other versions, but can't say for sure.