title: Java backend for browser extension (Firefox add-on)
body: <p>I intend to add visualization effects to <strong>existing web pages</strong>, powered by a MySQL database in the background. I assume this adding stuff to existing web pages requires writing a browser extension. </p>
  
  <p>For example, when Google returns search results, I want to customize the web page displaying (such as adding some bubble visualizations onto that page's blank places), the visualization is driven by data provided from the backend. </p>
  
  <p>Based on my knowledge, a typical <strong>web application</strong> involves JavaScript running on the frontend, Java backend. <strong>A web application will generate a brand-new web page normally, not adding new stuff into existing pages.</strong> The web server is supported by Java Servlet, Tomcat, etc. </p>
  
  <p>How can a browser extension (such as firefox add-on, chrome extension) talk to the backend Java programs? Is there existing template similar to Servlet/Tomcat that can do this job?</p>