Anything that opens "web pages" automatically uses the current app for opening web pages which can be FF. If you install FF it will prompt you and you can tap F

Anything that opens "web pages" automatically uses the current app for opening web pages which can be FF. If you install FF it will prompt you and you can tap FF and then tap "always" to skip the prompts. Many things like Facebook and Google search will initially use their own internal browsers for speed, unless you configure them not to. Even in an internal browser, you can generally reopen the page in FF.