Detect all Firefox versions in JS

This will detect any version of Firefox:

var isFirefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;

more specifically:

if(navigator.userAgent.toLowerCase().indexOf('firefox') > -1){
     // Do Firefox-related activities
}

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

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