I do that, too. cmd-J as shortcut to enable JavaScript without needing to reload. In my experience once I hardcode which websites I need JavaScript on, browsing becomes painless. And much faster obviously.
How do you set the shortcut? When I press cmd-j the Library in Firefox opens. I have checked "Disbale javascript" in settings in uBO. I guess that setting will be disable for just the site i visit when i click cmd-j?