One problem is that in .net each time you concat a string it has to allocate a new instance, do the concat operation and return to you a new string object ( if I am not mistaken). There is something called a string builder which helps with this problem. I would be interested to see the result when you use the string builder instead. Note that this problem is not a chrome problem but it is a fundamental aspect of the .net framework which will effect any .net language.