Using Firefox’s Web Console Editor Mode
While Scratchpad is no longer available, Mozilla did introduce a Web Console editor mode with Firefox 71+. This is a suitable alternative for writing and testing multi-line JavaScript. Here’s how to access it.
Open Tools > Web Developer > Web Console. You can also access the web console via the keyboard shortcut CTRL+SHIFT+K. The console appears at the bottom of the screen and shows the current web page’s code. Enter the multi-line editing mode by clicking the arrows on the lower left side of the console. You can also access multi-line editing via the keyboard shortcut Ctrl + B (Cmd + B on macOS). Type your code into the editor. Use Enter to add new lines, or use CTRL+Enter to run them.
