Beyond the default keyboard mouse defaults any changes to these defaults is user changed using 3rd party software and not part of the Browser defaults.

https://support.mozilla.org/en-US/kb/mouse-shortcuts-perform-common-tasks https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

If the website has its own context menu then you can hide the Firefox context menu via dom.event.contextmenu.enabled = true on the about:config page. If the pref is false then you always get the Firefox context menu, i.e. you may see two context menus, press ESC to close the Firefox context menu.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox