48ab3860bf
This patch adds an startup idle task that sets the browser as default if an attribution campaign id of "set_default_browser" is present on first run. This works supports an upcoming experiment where users will have the option to "download as default" via [[ https://www.mozilla.org/en-US/firefox/new/ | the stub installer marketing page ]]. Differential Revision: https://phabricator.services.mozilla.com/D225212