With Firefox and Edge I get this: If I use Opera Portable in Windows or Opera in Android, I have no problem accessing.
same here, but not in firefox. and i dont get that error message in firefox like edge (see left side).
Using Firefox snap on Kubuntu with uBlock Origin and custom Firefox settings, I have no issues at wizzair.com, selecting flights. Could it be your custom Firefox, or uBO, or other settings?
No problems here, using Firefox on Windows with uBlock Origin. I'm pretty sure it's got something to do with your very "special" FF and/or uBO settings. PS: ... and no problems with MS Edge, either.