Talvez o add-on SiteLauncher do Firefox ajude:
SiteLauncher is an add-on for Firefox that gives you a super-quick way to to open your favorite websites using only your keyboard. One special hotkey brings up the 'Launcher', followed by a unique key to launch a site.
Afirma-se que funciona corretamente para bookmarklets, mesmo que "Abrir atalhos na nova guia" esteja marcado.