Actually, no way to detect whether contextmenu is by mouse or touch (long tap) since `event.buttons` value is same value (although Chrome is different). If C++ code, we will be able to get event source type. [APZ caller](https://searchfox.org/mozilla-central/rev/4c8627a76e2e0a9b49c2b673424da478e08715ad/gfx/layers/apz/util/APZEventState.cpp#171-175) sets button is 2, and `WidgetMouseEvent`'s `ContextMenuTrigger` doesn't have long tap type. (If C++ code, we can get event source type.). But dom side will change event type for contextmenu by Bug 1675847, so after it, we can detect whether touch or mouse for contextmenu.
Bug 1879701 Comment 20 Edit History
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Actually, no way to detect whether contextmenu is by mouse or touch (long tap) since `event.buttons` value is same value (although Chrome is different). If C++ code, we will be able to get event source type. [APZ caller](https://searchfox.org/mozilla-central/rev/4c8627a76e2e0a9b49c2b673424da478e08715ad/gfx/layers/apz/util/APZEventState.cpp#171-175) sets button is 2, and `WidgetMouseEvent`'s `ContextMenuTrigger` doesn't have long tap type. But dom side will change event type for contextmenu by Bug 1675847, so after it, we can detect whether touch or mouse for contextmenu.