How do I get Selenium to populate a password field from a Firefox profile?

I have a username and password for a website saved in a Firefox profile.

I start selenium as

from selenium import webdriver 

profile_location = "/Users/admin/profile" # Firefox Profile
ff_profile = webdriver.FirefoxProfile(profile_location)

driver = webdriver.Firefox(ff_profile)
driver.get("http://www.example.com")

When I navigate to the website, the username is filled in the username field, but the password field is empty.

When I open Firefox without Selenium, both the username and password fields are filled in.

I've tried setting the network.automatic-ntlm-auth.trusted-uris preference to the website, but that doesn't help.

I've looked at questions like this one: How to automate username/password fill for firefox authentication popup using selenium IDE, but they don't quite address the problem that I'm facing.

Comparing Firefox about:config between normal Firefox and Selenium Firefox the only differences regarding password management are that the Selenium Firefox profile has browser.syncPromoViewsLeftMap and network.http.phishy-userpass-length preferences, and the normal Firefox profile does not have these preferences.