What did you do? ================ While updating my WebExtention, I was implementing contextMenus from https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/menus. The contextMenu can be created with an icon (image). When multiple menus items are created, they get put into a submenu. What happened? ============== The main menu item gets an icon (the specified icon that comes from the manifest). However, the submenu items cannot get icons. When specifying the icon property, the browser throws : "Error: Type error for parameter createProperties (Unexpected property "icons") for contextMenus.create." What should have happened? ========================== The submenu should have the capability to support icons. When using the Firefox Developer version, the browser does not throw the error, and it supports submenu icons. However, in the normal firefox 55.0.3, it doesn't work. Is there anything else we should know? ====================================== In the API, this is understood: https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/menus However, there is no reason not to add icons to submenus. Submenu icons have the potential to make menus more visually attractive and easier to use.

It is an enhancement.

Added in bug 1321544, see the docs or https://github.com/andymckay/sort-tabs-by-url/blob/master/background.js#L50-L66 for an example.