You can supplement these icons with others if you try sharing a page with other apps, but I don't think there's a way to just remove them. You can clear your app's cache and data, but that'll remove all your settings, bookmarks, history and logins. In the future, I suggest you should run a guest session before lending your phone/tablet to somebody else.

Hi. Just so we are clear.This is not an app/add-on/plugin. Look at my pictures.The Facebook,& Bluetooth icons were accidentally added by another user.When the other user accidentally tapped on/touched the share icons in the 2nd picture. There has to be a way to remove them.Mozilla would not make a stupid mistake like letting you add the icons,but not have a way to remove them! BTW,I did not give anyone permission to use my device.Someone just picked it up to move it,& while holding it by it's side accidentally squeezed/touched the screen.That's all it took.

The two most used share options are shown next to the share button. They don't transfer any information to the apps unless you click on them. There is not a way to remove items short of uninstalling the associated app. You can change the share icons by selecting a different service from the secondary menu. This might require several repetitions of selecting the same app to become the most used sharing item.