I don't think Firefox was reading any QR codes, but instead was recrawling the link in the "Recents" list on a new tab or bookmarks screen.
This is in no way a problem. There is precedent for browsers eagerly loading links, it happens all the time in regular webpages. This is most of the reason why anchors should be safe/side-effect free.
This is in no way a problem. There is precedent for browsers eagerly loading links, it happens all the time in regular webpages. This is most of the reason why anchors should be safe/side-effect free.