Not able to go full-screen in video players, like YouTube etc

### Describe the bug

Full-screen mode is broken due to lepton but works fine if customization settings are set to false. I was using the default `user.js`.

### Expected behavior

_No response_

### Screenshots

_No response_

### OS

Linux

### OS - Others

_No response_

### Firefox Version

129.0.1

### Distribution

- [X] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [ ] [Lepton's photon style](https://github.com/black7375/Firefox-UI-Fix/tree/photon-style)
- [ ] [Lepton's proton style](https://github.com/black7375/Firefox-UI-Fix/tree/proton-style)

### Theme

- [ ] Light
- [ ] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [X] System Default
- [ ] Others: (e.g. [Photon Colors](https://addons.mozilla.org/en-US/firefox/addon/photon-colors/), [Google Chrome Dark](https://addons.mozilla.org/en-US/firefox/addon/google-chrome-dark/), [Fairytale Of Nature](https://addons.mozilla.org/en-US/firefox/addon/fairytale-of-nature/))

### Theme - More Info

_No response_

### `user.js` setup

user.js setup

```javascript
// Your settings
```

### Additional context

_No response_

Start by reproducing the issue on Linux with Firefox 129.0.1, the Original Lepton distribution, the default user.js, and customization settings enabled, then compare with settings disabled. Done means full-screen playback works in video players such as YouTube without disabling customization.

Written by the indexing model from the issue text.