How can I know if browser is Chrome vs Firefox from web extension popup JavaScript?

Question

I am using the chrome namespace for both Chrome and Firefox, but would like to know which browser is running the web extension.

Answer 1

• Check chrome.app which is absent in Firefox:

  const isFirefox = !chrome.app;
  

• Check for browser which is absent in Chrome:

  const isFirefox = window.browser && browser.runtime;
  

  (the additional check is to avoid false positives on pages that have an element with id="browser" that creates a named property on window object for this element)

• Use the asynchronous browser.runtime.getBrowserInfo.

P.S. navigator.userAgent may be changed during debugging in devtools when switching to device mode or via about:config option in Firefox so it's an unreliable source.