Why Firefox Hid the Compact Mode Behind About:Config

In 2021, Mozilla released Firefox 89, introducing a major visual overhaul known as the Proton redesign that hid the popular "Compact" UI density option behind the advanced about:config menu. This article explains why Mozilla made the controversial decision to remove Compact mode from the standard settings menu, focusing on the company's goals to reduce development maintenance, rely on user telemetry data, and modernize the browser's interface, while still leaving the feature accessible for dedicated power users.

The Proton Redesign and Modern Aesthetics

The primary catalyst for hiding the Compact UI density was the introduction of the Proton design language. Mozilla aimed to modernize Firefox by replacing sharp edges and cramped toolbars with floating tabs, wider spacing, and simplified menus.

The goal was to improve readability and reduce accidental clicks for the average user, particularly on modern, high-resolution displays. Because Compact mode intentionally shrinks padding and squeezes interface elements together, it directly contradicted the core visual philosophy of the Proton update.

Low Usage Telemetry

Mozilla uses telemetry data to understand how people interact with Firefox. According to Mozilla's internal metrics prior to the redesign, a very small percentage of the overall user base actually used the Compact density setting.

Most users never change the default appearance of their browser. For Mozilla, maintaining a prominent setting in the customization menu for a feature that only a tiny fraction of people used contributed to unnecessary interface clutter.

Reducing Development and Maintenance Overhead

Before Firefox 89, developers had to support three distinct UI densities: Normal, Touch, and Compact. Every time Mozilla added a new button, menu, or visual feature, engineers and quality assurance teams had to design, code, and test it across all three modes across multiple operating systems (Windows, macOS, and Linux).

Compact mode often caused text clipping, alignment issues, and overlapping elements when new features were introduced. By officially deprecating the mode and hiding it, Mozilla significantly reduced the workload required to test and ship future updates.

The Compromise for Power Users

Originally, Mozilla planned to remove Compact mode entirely. However, during the testing phases of Firefox 89, a vocal segment of the community—particularly users with smaller laptop screens who needed to maximize vertical web page space—pushed back strongly against the removal.

As a compromise, Mozilla decided not to delete the code for Compact mode. Instead, they hid the toggle behind the about:config advanced preferences page and labeled the feature as "not supported" in the customization menu. This approach allowed power users to keep their preferred layout while freeing Mozilla from the obligation of fixing minor visual bugs associated with the cramped spacing.

How to Re-enable Compact Mode

Because the code still exists within the browser, users can easily restore the option to the Customize menu by following these steps:

  1. Type about:config into the Firefox address bar and press Enter.
  2. Click the button to accept the risk and continue.
  3. Type browser.compactmode.show into the search bar at the top.
  4. Click the toggle button on the right side of the result to change its value from false to true.
  5. Open the Firefox application menu, select More Tools, and click Customize Toolbar.
  6. Click the Density dropdown menu at the bottom of the screen and select Compact (not supported).