I have a weird behavior on firefox. When I righclick anywhere, a click event is fired over the contextual menu that is displayed. (this happens only in the document itself. Not in any menu or bar.
This means (according to my contextual menu at least) that any right click on a link opens the page in an incognito window, and any right click on an empty space triggers "save as"
I have disabled all extensions, but it still happens. For the time being I've resorted to holding right button and then selecting the desired option in the contextual menu.
(PD: I saw a similar question but the behavior is not quite the same)