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.
The setting is called "Relax blocking mode" and will enable JavaScript (but keep all ad blockers) if JavaScript is disabled by default.
In summary, for Firefox it’s under
about:addons > gear icon > Manage Extension Shortcuts
and for Chrome you can set it under chrome://extensions/shortcuts