Mac user here, only uses Safari. I keep getting this notice almost every time I do a flight search on united.com. Sometimes doing a search works, but most of the time I get this error message. I don't know why this keeps happening. I think I've done every trick in the book to try to resolve this issue. I've resetted my computer several times and I have also deleted all of my cookies, but that hasn't helped. I also have problems logging into my MP account as described earlier. For the record, united.com works completely fine on iOS Safari on my iPhone, including successfully logging into MP account.