I am just confirming this problem exists also on Xubuntu 18.04 and Firefox with the latest software updates as of to this date. At some point the Linux OS looses the reference point of the pop-up menu with respect to the right mouse click courser position, and it becomes permanently offsetted by a fixed amount of X and Y pixels. The mouse courser is offsetted by such amount of pixels and direction that it lands right on top of the pop-up menu first upper option, and upon releasing the mouse button it executes whatever operation appears in that menu position, see attached picture. In my case this anomaly appeared at some point on my newly installed Xubuntu 18.04 and inside the Firefox window web page. Xubuntu 18.04 came with Firefox 59 and at some point, probably after it run a software update (can't remember exact at what point the problem started) it had installed Firefox 60 when I noticed the problem within the browser. I had some problem with my Xubuntu install and reinstalled it again where it also would reinstall also the older Firefox version 59, the right-click offset was again gone, ran the software update and Firefox 60 got installed, the offset problem was back again. Today Firefox 61 update came and after the update the offset still persists. In the case of Firefox the following scenarios can occur: 1. Right click on web link will automatically open it up in a new tab, although the user might want to sellect another option from the menu. 2. Right click on an empty space inside a web page, would, if a previous web page have been opened, bring the user back to that page, although the user might want to sellect another option from the menu. --- After searching around on the net on this anomaly I came across the following web link below and in particular post #8, solved the offest problem temporary. "Mouse offset problem when using citrix" https://ubuntuforums.org/showthread.php?t=1214418&s=7a523455906cfff23926291a1a0b0775&p=10057080#post10057080 TEMPORARY SOLLUTION: What I did was to drag Firefox window in the corners so as to manually expand its window size to the maximum available desktop size, I then grabbed the window in the upper frame and "bounced" up to get the full window size (although I already had it at maximum window size), then dragged it back so as to "leave" full size, tried right clicking and the offset was gone. CAVEAT: Restarting Xubuntu will revert the mouse courser-menu offest, but by repeating the above mentioned procedure resolves the problem and seems to hold throughout the session until next restart. --- If possible, I would suggest the developers to introduce a quick fix that would at least prevent a right-click operation from performing a doubble operation, that is, separate the operation for right-click to bring up the pop-up menu from also executing any of the menu operations with a single right click, perhaps adding an opt-in/out right-click behavior option. Below some web links that might be relevant to the issue: https://bugs.launchpad.net/ubuntu/+source/gtk+2.0/+bug/410636 https://support.mozilla.org/en-US/questions/1210704 https://askubuntu.com/questions/18969/how-to-show-context-menu-when-right-click-released?s=1|243.4275 https://askubuntu.com/questions/916132/right-click-in-kde-opens-the-file-and-the-context-menu-at-the-same-time-on-the-d?s=2|103.7459 https://unix.stackexchange.com/questions/33519/how-to-make-x-less-sensitive-when-right-clicking https://unix.stackexchange.com/questions/60101/how-to-disable-select-on-release-right-mouse-button-in-linux?noredirect=1 https://gitlab.gnome.org/GNOME/gtk/issues/322 https://bugzilla.gnome.org/show_bug.cgi?id=591258 https://netbeans.org/bugzilla/show_bug.cgi?id=227754