Since it's happening for you on multiple computers and browsers, it may be wisest to try getting through to their technical support people (though there appears to be no website support number directly listed for their contacts). I'd start with pinging some of the options (chat, customer support request, etc) on their https://www.cheapoair.com/customersupport/ page until you can get hold of somebody that has website responsibilities or knows who does.
@tjrjn you are most welcome..
to me i'd say mouse is work 'n ok - ya already ruled out n e stuck keys and jammed mouse wheel since ya said it doesn't happened with other browsers..
so no virus stuff either my guess..
if it is not extensions.. What is do 'n this ! ?.. *i give up lol
does it happen if ya start opera in private mode..
ya might need to create a new profile