JSFiddle - React, Tailwind, and code Playground

HTML

<br>
<div id="about_me">
This Text color will be change
</div>

CSS

.red
{
    color: red;
}

.blue
{
    color: blue;
}

JavaScript

var userAgent = navigator.userAgent.toLocaleLowerCase();

if(userAgent.indexOf('firefox') > -1) {
    $("#about_me").addClass("red");
} else {
    $("#about_me").addClass("blue"); 
}