How can I make Firefox remember my proxy's username and password?

I'm using Firefox with a proxy. Every time I restart the browser, I have to enter the proxy's username and password.

Is there any way to get Firefox to remember the username and password and send it automatically so I don't have to type it in manually?

NTLM won't help as the proxy is unrelated to my Windows set-up.

I see this question was already asked. The accepted answer was to use FoxyProxy. This didn't solve my problem, however, as I was still prompted for the username and password the first time in the browsing session that I needed to use the proxy.

Solution 1:

1. Browse to about:config in Firefox
2. Click on "I'll be carefull, I promise!"

3. Search signon.autologin.proxy and network.websocket.enabled in the Search Input Box then change their values as follow:

   signon.autologin.proxy=true
   network.websocket.enabled=false
   

4. Restart Firefox, input user name and password for your proxy and click Remember.