This patch adds a new script -
`//browser_patches/firefox/repack-juggler.mjs`
This script lets you test Firefox changes if they are Juggler-specific
without firefox checkout / compilation.
The `repack-juggler.mjs` script does the following:
- downloads the latest build of Firefox-with-juggler
- finds an `omni.ja` file with Juggler files inside
- replaces juggler in omni.ja with the current juggler files in the index
