There is a little inconsistency between Chrome and Firefox with attributes selectors

For the two following examples, chrome could run it, but firefox not:

$('a[rel=nofollow]').on('click', function(event) {
	...
});

$('a[rel=nofollow"]').on('click', function(event) {
	...
});

Firefox stopped the script with error about unrecognized expression.

Finally what worked for both was

$("a[rel='nofollow']").on('click', function(event) {
	...
});