When your Firefox browser has more than 4 add-ons installed, if you go to Get Add-ons panel in Add-on Manager, Firefox shows custom add-on recommendations with “Recommended for you”? box, these add-ons can be unique to each user. Astonished! your installed add-ons are tracked and sent to Mozilla once a day to show them. Recommendations only appear when at least three add-ons are installed in the Firefox browser.
Mozilla introduced a new add-on manager in Firefox 4, where the “Get Add-ons” panel offers some useful information for beginners to customize their browser, like the “First time with add-ons” video (you might not have noticed this until now), Featured addons and themes (now personas) and links to browse them on the Mozilla addons site.
To update the above information, including add-on metadata, Firefox sends information about identifiers of add-ons you have installed and Firefox startup time with those add-ons installed in Mozilla. The add-on gallery returns updated Firefox add-on metadata information for you to view. Mozilla uses startup information to improve Firefox’s performance.
If you are concerned about your privacy and don’t want Firefox to send add-on identifiers to Mozilla, you can easily disable add-on recommendations, all you need to do is find extensions.getAddons.cache.enabled preference in about:config and change its value to false. Leaving that preference doesn’t hurt you either.