It can be nice to access your FF extension's variables/functions from the browser console (ctrl+shift+j) if you need some insight into its state.

It took me a while to figure this out, so I'm sharing it. Somewhere in your extension, do:

var chromewin = win_util.getMostRecentBrowserWindow();
chromewin.my_extension_state = ...;

Now in the browser console, you can access whatever variables you set in the global variable my_extension_state. In my case, I used it to assign a function that lets me evaluate code in the addon's background page. This lets me gain insight into the background page's variables and state straight from the browser console.

Note! This is a security hole. Only enable this when debugging your extension/addon. Disable it when you release it.

Note that this may or may not work on your device. If you're running into an app that works in a real browser but on in your Android's stock browser, do this:

1. Navigate to your app in the browser.
2. In the same tab go to about:debug
3. Reload (it may reload for you).
4. Profit.

This will show you errors that even window.onerror doesn't catch, which should help you narrow down your problem(s).

Source: This stackoverflow answer.