title: Exact difference between add-ons, plugins and extensions
body: <p>What is the exact difference between plugins, add-on and extensions.
  I have read a lot about this and confused, 
  For example see these four definitions:</p>
  
  <p>1-fire-fox says "Add-ons is the collective name for extensions, themes and plugins" (see <a href="https://support.mozilla.org/en-US/questions/790919" rel="noreferrer">https://support.mozilla.org/en-US/questions/790919</a>)</p>
  
  <p>2-www.Differencebetween.net says "Plug-in and Add-on are simply extensions ... Plug-in is the term that is usually used when referring to third party software (interact with a certain program) like flash player ... </p>
  
  <p>3- wikipedia (<a href="https://en.wikipedia.org/wiki/Plug-in_%28computing%29" rel="noreferrer">https://en.wikipedia.org/wiki/Plug-in_%28computing%29</a>) says plugin are being deprecated.</p>
  
  <p>4-I have read in another website that plugins are larger than add-ons and it consist add-on concept.</p>
  
  <p>Also I have read the answer provided in <a href="https://stackoverflow.com/questions/7575658/firefox-add-on-vs-extensions-vs-plugins">firefox add-on vs. extensions vs. plugins</a> and <a href="http://colonelpanic.net/2010/08/browser-plugins-vs-extensions-the-difference/" rel="noreferrer">http://colonelpanic.net/2010/08/browser-plugins-vs-extensions-the-difference/</a></p>
  
  <p>However I want to understand these differences especially in firebreath where plugins execute automatically through user's consent and add-on should install manually. Also I think plugin embed in htm page while add-on is in form of a separated file like xpi in fire-fox. </p>
  
  <p>Any exact, comprehensive and precise definitions for these three concepts which emerge differences would be appreciated.</p>