A limited set of FireFox add-ons are available in SmartCookieWeb Preview. If you would like another add-on already on the Mozilla add-on store to be included, just open an issue here. If you've made your own add-on and want it to be included in the browser, you should either upload it to Mozilla's add-on store and open an issue here, or submit the add-on for signing to Mozilla and open an issue with a link to the signed XPI file.
Contributions are greatly appreciated. Feel free to open an issue or pull request or help translate at (translate.cookiejarapps.com)