An event handler that will be called when an error occurs. This is most often because an invalid request ID was passed into webRequest.filterResponseData().

After this event is fired, the webRequest.StreamFilter.error property will contain a message giving more information about the error.

Note that this event is not triggered for network errors.

Browser compatibility

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ChromeEdgeFirefoxOperaFirefox for Android
onerrorChrome No support NoEdge No support NoFirefox Full support 57Opera No support NoFirefox Android Full support 57


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This example adds an onerror listener which logs the value of webRequest.StreamFilter.error.

function listener(details) {
  let filter = browser.webRequest.filterResponseData("12345");

  filter.onerror = event => {
    console.log(`Error: ${filter.error}`);

  //return {}; // not needed

  {urls: ["<all_urls>"], types: ["main_frame"]},

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