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Lepton (old name: Proton Fix)

Table of Contents

Does the theme not work after installation?

You should copy user.js file before the theme works.

The option system depends on user configuration, and nothing applies without settings.
Also, real-time changes are difficult because of technical limitations and require a restart.

Some settings can be conflicted and should be explicitly set to false.

Is your Firefox version v102 or lower?

You have to set userChrome.compatibility.accent_color to true additionally.


Proton is Firefoxs new design, starting from Firefox 89.
Photon is the old design of Firefox which was used until version 88.

Protons overall feel is good, but there were a few things I didnt like and wanted to improve.
Thats why this project was born, and Lepton to denote light theme layer.

Disclaimer: It works on Firefox 89 and above!!

Installation GuideScreenshotsTutorialOptionsCompatibility Issues SolutionTipsShow Off Your Config

(Leptons design 漎儭)

Feature List (Click)

  • Color
    • Default light/dark theme contrast enhancement
    • Colorful context menu
    • More dark mode support
    • Windows/Mac/Linux system theme support
    • Windows 7 compatibility
  • Icons
    • Panel
    • Context Menu
    • Global Menu
    • Librarys open context
    • Video Player
  • Padding Narrower
    • Tab
    • Panel
    • Menu
    • Density
    • Others
  • Tab Bar Layouts
    • Tabs on Bottom
    • One Liner
    • Vertical Tab Support
  • Tab Design
    • General:
      • Connect with toolbar (buttons like tabs)
    • Selected:
      • Box Shadow: Highlight the selected tab
      • Bottom Rounding: Natural
    • MultiSelected
      • Adjust Color: Easily recognizable
    • Unselect:
      • Divide Line: React to hover like chrome
    • Unloaded:
      • Dimmed: Looks like inactive
    • Clipped:
      • Clearer Text: Adjusted clipped gradation
      • Closed Button: Visible on hover
    • Sound:
      • Remove Second Label
      • Show Favicon: Always show favicon
      • PIP Icon
    • Container Tab:
      • Highlight line position: Displayed under tab
  • Button Design
    • New tab: Looks like tab
  • Activity Stream Design
    • Search Bar:
      • Focused Shadow: Same as the accent color
      • Hand off to Awesomebar
    • Icons:
      • Size: Fill (Changes dynamically to your size)
  • Error Page Design
    • Illustrations: Restore error page illustrations
  • Video Player
    • Background Style
    • Size at fullscreen
  • Fullscreen
    • Overlap mode
  • Others
    • Animations
    • Hidden & Auto Hide
    • Activate calculator at address bar
    • Mouse pointer for each context

Installation Guide

Installation script (experimental)

Linux/Mac users:

bash -c "$(curl -fsSL"

Windows users: Run with powershell (Does not work at Win7?)

Powershell -c "Set-ExecutionPolicy Bypass -Scope Process -Force; [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol -bor 3072; iwr -useb | iex"

Manual Installation

You can see the installation guide with screenshots on the wiki.

  1. Download files
    • Click the green :arrow_down: Code button above
    • Select :package: Download ZIP
  2. Find your profile directory
    • Open about:support in a new tab
    • Find the Profile Directory(Linux) / Profile Folder(Windows) entry
    • Click the Open Directory(Linux) / Open Folder(Windows) button
  3. Copy downloaded files
    • Extract the downloaded zip file
    • Copy the user.js file to the previously opened profile directory
    • Create a new directory inside your profile directory called chrome
    • Copy the remaining files from the extracted zip-file into previously created the chrome directory
  4. Restart Firefox
    • Click the Clear startup cache at the top of about:support

If you prefer Photon, see Leptons photon-style.
If you prefer Proton, see Leptons proton-style.

WHY Proton?

I think a lot has improved.

(Protons design 漎儭)

  • Neatly organized menu
  • Icon beautiful enough to remind you of Edge
  • Nice color scheme
  • Satisfied Rounding
  • Modal window & Scrollbar!!

WHY Not Proton?

However, there are also many flaws.

(Photons design 漎儭)

  • Is it a tab or a button?
  • Where are the menu icons?
  • Icons in ActivityStream are too small
  • Padding gaps are wide
  • Address bar 3-point menu, screenshot moves to toolbar (cant fix)

Padding Comparisons

  • Photon (Quantum)
  • Proton
  • Lepton

Sponsors & Contributors

Thanks to all sponsors & contributors to this project for providing help and developing features!


  • A donation was received from Safira on Ko-Fi
  • Private sponsors: 3


A list of all contributors can be found in CREDITS.

Bug / Questions?

If you found a bug, please contact issue.
If you have any questions or inquiries, please contact discussions.


  • Black pixels around the selected tab bottom corners

Please follow the Installation Guide,
or set about:configs svg.context-properties.content.enabled to true .

  • The closed button and some panel menu icons are not visible.

Please follow the Installation Guide,
or copy the icons directory to chrome .

  • Less icons in the panel with photon-style

    I didnt put all the icons like before.