Targeting only Firefox with CSS

Updated(from @Antoine comment)

You can use @supports

@supports (-moz-appearance:none) {
    h1 { color:red; } 
}

<h1>This should be red in FF</h1>

More on @supports here

OK, I've found it. This is probably the cleanest and easiest solution out there and does not rely on JavaScript being turned on.

@-moz-document url-prefix() {
  h1 {
    color: red;
  }
}

<h1>This should be red in FF</h1>

It's based on yet another Mozilla specific CSS extension. There's a whole list for these CSS extensions right here: Mozilla CSS Extensions.

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