Firefox JSTerm v2 is available.

JSTerm:

• Install Addon (Firefox 16+);
• on github;
• report bugs here.

Changelog:

• performance improvements;
• can undock the terminal in its own window;
• native osx fullscreen support (see screencast);
• global history (shared across sessions);
• better multi-line support;
• added $ and $$ methods;
• more keybindings (see :help)

JSTerm is an experimental restartless addon. It adds a "jsterm" button in the developer Toolbar (Firefox 16+). The terminal behaves like a shell terminal (history, completion on tab, key bindings, …). It's a classic REPL environnement. It uses the builtin Firefox Source Editor to highlight JavaScript. It uses a Sandbox to eval JavaScript. And it comes with an Object Inspector.

For Firefox and Addons developers: like Scratchpad, this tool comes with a "chrome" mode (type ":chrome" to enable it).