Lumen: Ambient Light & Original YouTube Audio by Simon

Lumen puts an ambient light around YouTube videos, plays them in their original language and starts each one in the quality, speed and volume you choose. It can also hide the parts of YouTube you don't need.

Ambient Light
The page around the player takes on the colors at the edges of the video, like a TV with backlighting. The light follows the picture smoothly and changes at once at scene cuts.
• Works in default view and theater mode, with vertical videos and live streams
• Dark scenes stay black, which suits OLED screens
• The search bar and the playlist beside the video let the light shine through
• The page below the video gets a little darker, so comments stay easy to read
• Brightness, color, reach, softness and smoothing can be adjusted
• Alt+A turns the light on or off

Sound and Picture
• Volume from 0 to 300%, for quiet videos and weak laptop speakers
• Video brightness from 100% down to 0%, for example at night. The light dims along with it

Original Language
• Dubbed videos play with the original voice
• Titles and thumbnails as the channel made them, instead of YouTube's automatic translations: on the video page, in fullscreen, in the tab, in search, the home feed, the sidebar, playlists and Shorts shelves

Playback
• Every video starts in the resolution you choose, from 144p to 4320p, or always in the highest available
• Every video starts at the speed you choose, from 0.5× to 2×. Ads and live streams keep their normal speed
• Prefer 60 fps or limit to 30 fps
• Uses the enhanced bitrate of YouTube Premium if your account has it
• Picking a different quality or speed in YouTube still works for that video
• Can avoid AV1 or VP9 on devices without hardware decoding for them
• Can also apply to YouTube videos embedded on other websites

Clean-Up
• Shorts can stay as they are, play as normal videos with light, quality and speed, or be hidden everywhere
• Hide the recommendations beside the video, the comments or the home feed
• Hide end cards, the suggestions at the end of a video and info cards

Good to Know
• All settings are in one small menu. Hovering a setting explains it, right-clicking resets it
• Lumen's toolbar icon shows at a glance whether the light is on, the video is dimmed or the volume has been changed
• Settings follow you to your other devices through Firefox Sync, and a backup file keeps them safe
• Packed with features, yet lightweight: the video player loads first and scrolling stays smooth
• The light needs hardware acceleration in Firefox and YouTube's dark theme. The menu shows when something is missing
• Lumen checks its main features. If a YouTube update breaks one, the menu says which, and the rest keeps working

Privacy
Lumen only runs on YouTube and collects no data. For original titles and thumbnails it asks YouTube itself and connects to nothing else. Settings are stored in Firefox and synced to your other devices if Firefox syncs your add-ons.

Lumen is an independent project and is not affiliated with YouTube or Google.

I first built Lumen for myself, and I hope you enjoy it as much as I do. If you like it, a short review would mean a lot!