'Adding custom build to Firefox' poor documented

### Describe the bug

Following the instructions on https://github.com/MetaMask/metamask-extension/blob/develop/docs/add-to-firefox.md results in a non functional metamask. The extension is not added to the browser at all

### Steps to reproduce

1. Checkout the source code from https://github.com/MetaMask/metamask-extension/tree/v10.11.1
2. Edit ```.metamaskrc.dist``` , put in with my Infura ID
3. yarn setup
4. yarn start
5. Followed https://github.com/MetaMask/metamask-extension/blob/develop/docs/add-to-firefox.md
Result: blank page. The extension icon is not even added to the toolbar, I need to manually go to moz-extension:///home.html
6. It doesn't show anything

### Error messages or log output

_No response_

### Version

10.11.1

### Build type

Other (please specify exactly where you obtained this build in "Additional Context" section)

### Browser

Firefox

### Operating system

MacOS

### Hardware wallet

_No response_

### Additional context

_No response_

Start with docs/add-to-firefox.md and reproduce the reported steps using the v10.11.1 source on Firefox and macOS. Verify whether the documented build and loading steps still work; done means the documentation clearly produces a visible, functional extension rather than a blank page or requiring a manual moz-extension URL.

Written by the indexing model from the issue text.