I could almost see this as another stamp your feet and blame the other person type thing again.
Apple may be adhering 100% to some rules and perhaps the Tesco site in some tiny way breaks some rule and bombs the browser out.
You could then handle this two ways. You can tweak the browser to not crash and perhaps "soak up" the error and carry on working.
Or you can stand your ground, say your browser is right, blame Tesco and say they should change their site so it works.
It may not be this, but it could be.
Ideally you work together to get over the problem, which if of course best for the consumer.