I am using Firefox (48.0), Xubuntu (16.04), Xfce (4.12.1) on a Macbook (mid 2007). When right clicking using two fingers on the trackpad no context menu is shown. The trackpad consist of a pad, and a single button. Right clicking with two fingers works in other applications (e.g. Terminal). That is a context menu pops up. Right clicking works in Firefox when using an external mouse (and using the external mouse to right click). I am using a clean install of Firefox (and of Xubuntu). I have disabled hardware acceleration, used a new profile and tried safe mode, all without success. There are no extensions installed (except those installed by Mozilla and Ubuntu) When displaying an html page containing javascript code: "div.addEventListener("contextmenu", function(e) { ... }, false);", context menu events are registered, but no context menu is shown (when using the external mouse the context menu is shown). If I open a web page, put two fingers on the trackpad, repeatedly click the mouse button, and occasionally scroll up and down, the context menu shows up very seldom at random. I am only able to do this when smooth scrolling is enabled. No context menu is shown when right clicking tabs. There is a context menu when right clicking the title of the Firefox window, but I guess that belongs to Xfce. I have tried disabling two finger scrolling in Xfce. If I change from right hand to left hand mode in the mouse settings of Xfce (which is somewhat ridiculous for this kind of trackpad), the context menu is shown for all clicks.