fm3

/* To enable changing tabs by using the mouse wheel,
 * enter this code into the browser console (Ctrl+Shift+J) */

var onTabWheel = function(ev) {
  if (ev.deltaMode == 1 /* DOM_DELTA_LINE */) {
    var idx = gBrowser.tabContainer.getIndexOfItem(gBrowser.selectedTab);
    var direction = ev.deltaY > 0 ? 1 : -1;
    gBrowser.selectTabAtIndex((idx + direction) % gBrowser.tabs.length);
  }
}

fm3

#MaxHotkeysPerInterval 200
shouldFire()
{
CoordMode, Mouse, Screen
MouseGetPos, mouseX, mouseY, MouseHoverWin
WinGetPos, winX, winY, width, height, ahk_id %MouseHoverWin%
WinGetClass, class, ahk_id %MouseHoverWin%
if (mouseY - winY >= 0 && mouseY - winY < 40 && class == "MozillaWindowClass") {
	return 1
}