Browsers crash when loading a page with payment data

Hi everybody,
i've been trying to book a flight since yesterday and every time the browsers crash when the last step has arrived, where you have to enter the payment details.
I booked a Ryanair flight before. No problems there. Now it's Vueling. I try with both Midori and Webbrowser and it's the same with both of them. I can pass the first steps, enter my details and choose options, but when the last page loads, the browsers tell me there is a problem and stop loading the page. I even allowed them to accept ads and popups and to not tell the site that i don't want to be tracked.
The problem happens also at another flight booking site.
Any ideas about what is behind this problem?