Two articles on web tracking of users on the Internet.
https://windowssecrets.com/newsletter/youre-being-followed-how-to-block-web-tracking/#story1
https://windowssecrets.com/newsletter/add-ons-that-help-browsers-block-web-trackers/#story1
Some comments on two Firefox tracking blockers Add-ons:
Disconnect
Install it first before other Firefox web track blockers.
It is not available on the Mozilla Firefox Add-on web site.
Ghostery
You need to configure it to block the web trackers, then save the settings.
Ghostery Update: Nov 8, 2013
When Ghostery provides an add-on update, you need to click on the Ghostery icon then
the cog wheel icon (settings)
Options
scroll down to Trackers
Select All
Save