Disable a Browser's Built-in Password Manager

In Firefox, navigate to Preferences → Privacy & Security and scroll down to the Logins and Passwords section. In this section, uncheck all the pre-checked options:

You should also find out which logins Firefox has already saved by selecting the Saved Logins... button:

If you haven't already saved these passwords in Bitwarden, export them for future import to Bitwarden. Once exported, you should  Remove these passwords from Firefox.

In Safari, open Settings from the menu bar and navigate to the AutoFill tab. On this tab, uncheck all the pre-checked options:

You should also find out which passwords Safari has already saved by navigating to the Passwords tab. If you have passwords saved, this tab will lead you to the Apple Passwords app.

If you haven't already saved these passwords in Bitwarden, create login items in Bitwarden for these passwords. Once all saved passwords are in Bitwarden, Remove these passwords from Safari.

In Vivaldi, open the  Vivaldi Settings window and select  Privacy from the left-hand navigation. Scroll down to the Passwords section and uncheck the Save Webpage Passwords option:

You should also find out which passwords Vivaldi has already saved by selecting the Show Saved Passwords button:

If you haven't already saved these passwords in Bitwarden, create login items in Bitwarden for these passwords. Once all saved passwords are in Bitwarden, remove these passwords from Vivaldi. Learn how.

Despite sharing roots with Firefox, Tor is unique in that it doesn't save your logins by default. If you haven't manually configured Tor to save and autofill logins, you are already all set.

If you did, navigate to the Passwords page by entering about:preferences#privacy in the address bar, and scroll down to the Logins and Passwords section. Toggle off all the options that you had checked:

You should also find out which logins Tor has already saved by selecting the Saved Logins... button:

If you haven't already saved these passwords in Bitwarden, create login items in Bitwarden for these passwords. Once all saved passwords are in Bitwarden,  Remove these passwords from Tor.

In DuckDuckGo, navigate to Settings → Autofill. From this screen, uncheck the box for Usernames and passwords.

You can create a backup of your existing data by selecting Export Passwords. Once you have created a backup file, select View Autofill Content... and delete the stored autofill data to remove previously saved suggestions.

In the Password Manager section, macOS users can choose to use Bitwarden. Learn more about the Bitwarden DuckDuckGo macOS browser integration here.