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HAR Export Trigger

On November 14, with the launch of Firefox Quantum (AKA 57), support for old school extensions will stop in Firefox. It means that this extension will no longer work. New version of this extension built on top of WebExtensions API is available here:

Firefox add-on improving automated HAR (HTTP Archive) export of collected data from the Network panel. This add-on is built on top of native developer tools in Firefox. Firebug is not needed for this add-on.

The add-on exports HAR API directly to the page. Any automated system can be consequently built on top of the API and trigger HAR export using a simple JavaScript call at any time. It can be also nicely integrated with e.g. Selenium to implement automated HAR export robots for existing automated test suites.

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HAR Export Trigger is free and open source software distributed under the BSD License.


You need Firefox 42+ to run this extension.


See the latest release

How To Use

This extension exposes HAR API into the content allowing pages to trigger HAR export as needed. To ensure that API is properly exposed into the page content you need to yet set the following preference in your Firefox profile (any string value that is passed into API calls):


To start automated collecting of HTTP data you need to set the following preference to true:


You might also want to set the following preference to true, so the developer Toolbox doesn't have to be opened.


An example script on your page can look like as follows:

var options = {
  token: "test",      // Value of the token in your preferences
  getData: true,      // True if you want to get HAR data as a string

HAR.triggerExport(options).then(result => {

Build & Run HAR Export Trigger

Following instructions describe how to build the extension from the source and run on your machine.

  1. Install JPM: npm install jpm -g (read more about installing jpm)
  2. Get the source: git clone
  3. Install required NPM modules: npm install
  4. Run jpm run -b nightly in the source directory (learn more about jpm commands)

Further Resources