To install **Firefox with Widevine support** on **Debian** using **Nix**, follow these steps:

### 1. **Install Firefox via Nix**
Install Firefox from the `nixpkgs` repository:

```sh
nix-env -iA nixpkgs.firefox
```

### 2. **Enable Widevine DRM in Firefox**
Widevine is a **proprietary DRM module**, so Firefox doesn’t ship it by default in Nix. To enable it, you need to:

#### **a) Allow DRM Content in Firefox**
- Open Firefox and go to: `about:preferences`
- Scroll to **Digital Rights Management (DRM) Content**
- Enable **Play DRM-controlled content**

#### **b) Install Widevine Plugin**
Nix provides **widevine** as a separate package, but Firefox may not recognize it automatically. Install it with:

```sh
nix-env -iA nixpkgs.widevine-cdm
```

#### **c) Manually Link Widevine**
Since Firefox installed via Nix is sandboxed, you may need to manually create a symlink:

```sh
mkdir -p ~/.mozilla/plugins
ln -s ~/.nix-profile/lib/mozilla/plugins/libwidevinecdm.so ~/.mozilla/plugins/
```

#### **d) Verify Widevine Installation**
- Open **`about:plugins`** in Firefox.
- Look for **Widevine Content Decryption Module**.

#### **e) Test DRM Video**
Try playing DRM-protected content (e.g., [Netflix](https://www.netflix.com) or [Spotify Web Player](https://open.spotify.com/)). If it doesn’t work:
- Restart Firefox.
- Ensure `widevine-cdm` is enabled under `about:addons` → **Plugins**.

This setup should allow Firefox to use **Widevine DRM** for streaming services like Netflix, Amazon Prime, and Spotify. 🚀