What I meant is that in Firefox [mouse-3] on a tab pops up a menu of
tab-related actions other than activating a tab as [mouse-1] does.
Also [mouse-3] on a link pops up a menu of link-related actions,
on an image - a menu of image-related actions and so on. Emacs could do
the same for the toolbar icons. Even in Firefox [mouse-3] on the [Back]
toolbar button displays a list of all previous nodes.
I for one dislike that. For example, the normal mouse-3 menu in Firefox
has "Reload" and "Back", which I use from time to time. But if you happen
to be over a link or an image when you click mouse-3, there is no "Back"
or "Reload" in those menus. Quite annoying.