Tracking Stop Button

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One of most used features on the browser (other then the back button) is the stop button. It stops a page from loading and its really helpful if you are about to load a huge page. This page is created to show how clicking the Stop button calls a Stop() function dowing inside the dark depths of the Firefox core.


  • Mark Paruzel
  • Yi (Eric) Shen

Steps Taken

  • I started off with the tooltip that is displayed when a user hovers over the Stop button. The tool tip shows the string "Stop loading this page". So I jumped into LXR and started searching for this string.
  • I found this page that shows that the tooltip is part of an object called browse_stop. This is all defined inside an XML document that defines the layout of the toolbar.
  • Searching for browse_stop, I found a bunch of documents using it. One of the links that jumped out at me was this one which displays the javascript that handles the event of someone clicking on the stop button.
  • Inside the OnBrowserStop function, there is a line that calls the Stop() function of an nsCOMPtr object. So its safe to conclude that the actual code that Stops the rendering of a page is located inside a COM Object.


It is very hard to actually understand every single technology that Firefox uses but from just searching for a simple thing such as a Stop button, you can easily narrow the specific technologies that are in use by the stop button.