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I was amending the order that's due to be delivered tomorrow. I think it's a problem at the tesco end as I kept getting 'it's not your fault, just press the reset button. I think in the end I did make the changes; though I haven't received the usual confirmation, they are showing on my account. I also succeeded in booking a slot for two weeks' time, for which I did get an acknowledgement.
I'm still using Google Chrome, though I do have firefox installed. Running Windows 7 - might this be the problem?