Http links are to web browsers. If Amazon or eBay developed new protocols, the links wouldn't be to http:// they'd be to something else. for instance, for International Relay Chat, the link starts irc://, for file transfer it starts
ftp://. If the links she's sending you begin
http://, that says "feed this to a web browser", so it won't open a different app. (Neither Amazon's app oe eBay's app are web browsers.) But Opera probably opens to the right page. (If it doesn't, she's sending you links to the site's landing page, like amazon.com or ebay.com.)