Firefox-specific actions aren't necessary by default on Windows/macOS

On Windows and macOS, Firefox imports third-party roots from the OS by default (`security.enterprise_roots.enabled` in `about:config`), so it shouldn't be necessary to do anything extra in most cases. It would be nice if this were mentioned somewhere.

Find the existing documentation covering Firefox on Windows and macOS, then verify the stated behavior in Firefox's about:config setting security.enterprise_roots.enabled. Done means the relevant documentation clearly explains that extra Firefox-specific actions are usually unnecessary on those operating systems.

Written by the indexing model from the issue text.