Safari doesn't work with Sainsburys online ordering

Just before Christmas I lost my Sainsbury's shopping slot as Safari crashed whilst I was on their site. This apparently deleted my order as it took over 2 hours to get back on. I have tried a few times since with the same problem (temporarily getting on before crashing) and Sainsbury's keep saying that the fault lies with Safari. I have used my MacBook with Safari for over a year now on Sainsbury's and have never had a problem up until then. Can anyone lend some advice if this is a Safari problem and if so what can I do about it?

Thanks