mozIStoragePendingStatement interface represents a pending asynchronous database statement, and offers the
cancel() method which allows you to cancel the pending statement.
Cancels the pending statement. Fails only if you attempt to cancel the operation more than once.
SELECT, once you cancel the statement, you will receive no further notifications about results.
In versions of Gecko prior to Gecko 1.9.2, this returned a boolean value that was
true if the query was canceled successfully or
false if not. Starting with Gecko 1.9.2, this information is no longer provided and the method doesn't return a value.