JavaScript Toggle On and Off (WebExtension) v0.2.4 
JavaScript Toggle On and Off add-on brings a bulletproof method to disable JavaScript execution in both standard and private modes. Note that after installation JavaScript execution is enabled, you need to click the toolbar button to disable the execution.
This is the WebExtension version of my JavaScript Toggle On and Off add-on. This version supports white-listing domains, but it is a bit less powerful but still reliable.
Default hotkey (shortcut) to toggle JS engine on and off is "Alt + Shift + L." Still, there is no UI to edit this default shortcut. This should be offered by Firefox.
For more info about the extension, please visit:
https://add0n.com/javascript-toggler.html
For bug reports, you can submit yours to:
https://github.com/rNeomy/javascript-toggle-on-and-off/issues
To check your browser's JavaScript support (inline, data URI, external, iframe, document.write, ...) use:
https://webbrowsertools.com/javascript/
What types are supported:
1. Inline JavaScript on top and frame elements
2. Data URI JavaScript on top and frame elements
3. External JavaScript on top and frame elements
4. Inline events
5. "javascript:" URIs
6. setTimeout evaluation
7. document.write execution