Before using your income tax refund to pay down your mortgage, look at your complete financial picture.
If you have other debts with higher interest rates, it may make more sense to allocate your refund to pay those down or off first.
If you have contribution room in your RRSPs and no other debts, it may make more sense to put your refund toward your registered accounts to reduce your taxable income for the following tax year.
If you have a healthy amount of savings, max out your contribution room every year, and have no other debts, it could make sense to put your income tax refund toward your mortgage.