Firefox has a feature to get around sites that try to block the context menu. If you do Shift-right click, then the page cannot block that and Firefox will always show the context menu. Unfortunately, this doesn't work well with ThinLinc as we want to propagate that event. Noticed upstream: https://github.com/novnc/noVNC/issues/1717 And a bug for this already exists with Mozilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1467158 The other browsers don't seem to have this problem.
