Firefox does not have an ads system. How ironic that a browser meant to be a privacy-friendly browser with strong ad-blocking abilities has a by-default-enabled ad system....
Firefox has an ad system, personalized from the browsing history, which is default enabled in a number of countries that grows with the version number:
https://www.mozilla.org/en-US/privacy/firefox/
We recommend content to you based on your browsing history, language, and country location.
We also share aggregated data about the sponsored content you see and click with our third-party ad platform Adzerk
I agree that it's ironic.
Firefox has addon support on mobile devices.
Only a few addons are supported in the last version.