If you´re using robotframework with or without RIDE IDE, this suggestion actually works for me In conjunction with Saved Password Editor
Generate a new firefox profile by starting the ff profile manager (dos prompt: ff.exe -p)
Start ff with this profile
Install the add-on Auto-auth, (which allows you to log on automatically on sites with basic auth when you have stored the credentials in the password manager of ff; without this add-on, for every new session you will get prompted for the credentials, even if you stored them in the password manager.)
Goto your website, fill in the credentials, and save them in the password manager
Use this profile to run your robotframework tests: start the selenium server standalone with the option -firefoxProfileTemplate 'C:\Program Files (x86)\Mozilla Firefox...\path_to_this_new_profile'