Question

How to detect Firefox in JavaScript?
I want to detect all versions of Firefox.

Answer 1

This will detect any version of Firefox:

const isFirefox = navigator.userAgent.toLowerCase().includes('firefox');

if (isFirefox) {
  console.log("Your browser is Firefox");
} else {
  console.log("Your browser is not Firefox");
}

You may want to consider using feature-detection ala Modernizr, or a related tool, to accomplish what you need.