Profanity Filter WebExtension

A Firefox WebExtension that automatically detects profanity in subtitles, mutes audio during profanity, and displays censored subtitles overlaying the video.

Features

• Subtitle Upload: Load SRT, ASS, or WEBVTT subtitle files
• Auto-Detection: Automatically detects subtitles on supported streaming sites
• Profanity Detection: Multi-layered detection using:
  • Wordlist matching (exact)
  • Obfuscation patterns (regex)
  • Fuzzy matching (Levenshtein distance)
  • Context-aware filtering (religious terms whitelist)
• Audio Control: Automatically mute the tab when profanity is detected
• Censored Overlay: Display subtitles with profanity replaced by [CENSORED] or fun alternatives
• Timing Sync: Adjust subtitle timing with real-time preview
• Privacy-First: All processing happens locally in your browser

Supported Sites

The extension can automatically detect and extract subtitles from:

• YouTube (auto-generated and uploaded captions)
• Jellyfin (local and remote instances, HLS streams, native and embedded subtitles)
• LookMovie
• FMovies
• PlutoTV (partial)
• 123Chill (partial)

Installation

From Source

1. Clone this repository
2. Run npm install to install dependencies
3. Run npm run build to build the extension
4. Open Firefox and navigate to about:debugging
5. Click "This Firefox" → "Load Temporary Add-on"
6. Select the manifest file from the dist folder

For Production (Signed XPI)

npm run package

This creates artifacts/ffprofanity-1.0.0.xpi for distribution.

Development

npm run dev        # Build for development
npm run build      # Build for production (creates XPI)
npm run test       # Run test suite
npm run test:watch # Run tests in watch mode

Project Structure

src/
├── background/       # Service worker (mute control, message routing)
├── content/          # Content script (overlay rendering, video sync)
├── popup/            # Toolbar popup UI
├── options/          # Settings page UI
├── extractors/       # Site-specific subtitle extractors
├── page-scripts/     # Injected scripts for streaming sites
└── lib/              # Core libraries
    ├── detector.ts   # Profanity detection engine
    ├── parser.ts     # Subtitle format parsers (SRT/VTT/ASS)
    ├── cueIndex.ts   # O(log n) time-based lookup
    ├── storage.ts    # Extension storage helpers
    ├── substitutions.ts # Fun word replacements
    └── wordlist.ts   # Profanity wordlist

Tech Stack

• Language: TypeScript
• Build: esbuild (fast bundling)
• Test: Vitest with jsdom
• Platform: Firefox WebExtension Manifest V3

Usage

1. Click the extension icon to open the popup
2. Click "Options" to open the settings page
3. Upload your subtitle file (SRT, ASS, or WEBVTT) - or use auto-detection
4. Adjust the profanity detection sensitivity:
   • High: Mute entire caption when profanity detected
   • Medium: Mute only the profanity word (balanced buffering)
   • Low: Mute only the profanity word (minimal buffering)
5. Choose substitution style:
   • [CENSORED] text
   • Fun alternatives (silly, polite, random, monkeys)
6. Use the offset slider to sync subtitles with video
7. Play your video and enjoy profanity-free viewing

Keyboard Shortcuts

Shortcut	Action
Alt+Left	Decrease subtitle offset
Alt+Right	Increase subtitle offset

Testing

The project has 109 tests covering:

• Subtitle parsing (SRT, VTT, ASS formats)
• Profanity detection (exact, fuzzy, obfuscation patterns)
• Profanity window timing calculations
• Cue index time-based lookups

npm run test

Privacy

This extension is designed with privacy as the primary concern:

• No external servers: All subtitle processing is done locally
• No telemetry: No usage data is sent anywhere
• No network calls: The extension works completely offline
• Local storage only: Settings and subtitles are stored in browser storage
• No tracking: No analytics or third-party scripts

Permissions

The extension requests minimal permissions:

Permission	Purpose
storage	Save settings and subtitles
tabs	Mute/unmute tab audio
activeTab	Access current tab for overlay
webNavigation	Detect page loads for auto-extraction
webRequest	Intercept subtitle network requests

License

MIT License - see LICENSE file for details.