1) Firefox Hello (Smiley Icon) :

Description : As per Mozilla website Firefox Hello lets you make free (as in gratis) video and voice calls directly from the browser. The Application initiates a VOIP session, generates a link and sharing the link invites anyone to join the session.

Solution :

Clear the Value of the following Preferences or change them to "false" to successfully disable Firefox Hello.

loop.enabled {false}
loop.feedback.baseUrl {}
loop.gettingStarted.url; {}
loop.learnMoreUrl {}
loop.legal.ToS_url {}
loop.legal.privacy_url {}
loop.oauth.google.redirect_uri {}
loop.oauth.google.scope {}
loop.server {}
loop.soft_start_hostname {}
loop.support_url {}
loop.throttled2 {false}

2) Firefox Share (Paper Rocket Icon) :

Description : Related to Firefox Social. social.share.activationPanelEnabled has been set to "false" already which makes the service unnecessary. Setting social.share.activationPanelEnabled to "true" reveals the true nature of the service to share with services like Facebook, Google Plus, Twitter, Linkedin Etc.

Solution :

Clear the Value of the following preference to completely disable association with above services making the button useless.

social.shareDirectory {}

3) Discover Apps (Rocket Icon) :

Description : Links to Firefox Marketplace (Requires JS)

Solution :

Clear the Value of the following preference

browser.apps.URL {}