The extension does have the option to disable caching of JavaScript from selected hosts (https://addons.mozilla.org/user-media/previews/full/244/244875.png), but if you find it unreliable, there is an internal option:

Open the Developer Tools, change to the Network panel, and check the box for Disable Cache. You can undock the Dev Tools to a separate window while you work so you have use of the full height of the tab.