the way you did it should work in chrome but nvm.Here is another way
select = $('#custcol7');
select.find('option[value=["'+sizeValue +'"]').remove();
and if you want to show it again:
select.append('<option value="'+sizeValue+'"></option>');
It works perfectly on every browser and its really simple code. The problem is if you want to hide several options it is more typing .. but that can be solved by putting them into variables if they don't change dynamically like that :
var options = '<option value="'+sizeValue1+'"></option><option value="'+sizeValue2+'"></option><option value="'+sizeValue3+'"></option>';
select.append(options);
This way if you have to remove/append on several places you only typed the options once.Hope i gave another interesting option. Best Regards.