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This patch changes the backing prefs by relying on the tristate offered
by browser.display.document_color_use instead of
browser.display.use_system_colors. This simplifies the color
decision tree, and offers a simplified UI.
The tristate preference offered to the user is as follows:
1. "Use platform's contrast settings" (document_color_use=0)
2. "Off" - never use HCM, regardless of platform setting (document_color_use=1)
3. "On" - always use HCM, regardless of platform setting (document_color_use=2)
Option 3 also reveals a colors UI for the user to choose the palette the
browser HCM will use (bg/text/link/visited).
There are three color palettes to choose from in light of the preference
above they are:
1. WIDGET_COLORS: The OS's configured colors used by its theme.
2. HARDCODED_COLORS: Colors deemed as standard and are hard coded into
Firefox (eg. white on black text, blue and purple links).
3. PREFERENCE_COLORS: Colors that are stored in preferences and are
configurable from the colors UI (eg. browser.visited_color and
browser.display.background_color)
The decision over which palette to use is as follows:
* If we are styling browser UI -> WIDGET_COLORS
* else, if resist fingerprinting is enabled -> HARDCODED_COLORS
* else, if document_color_use==0 AND OS HCM is on -> WIDGET_COLORS
* else, if document_color_use==2 -> PREFERENCE_COLORS
* else -> HARDCODED_COLORS
Differential Revision: https://phabricator.services.mozilla.com/D211115
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HCM Settings
Several Firefox settings work together to determine how web content and browser chrome are rendered. They can be hard to keep track of! Use the flowcharts below for quick reference.
Settings that control color usage in browser chrome
- OS HCM:
- Windows: High Contrast Mode in OS accessibility settings
- macOS: Increase Contrast in OS accessibility settings
- Linux: High Contrast Theme in OS accessibility settings
- FF Theme (AKA FF Colorway) Note: OS HCM settings will only trigger HCM color usage in chrome if a user's FF theme is set to "system auto". If they have a pre-selected colorway or other FF theme (including explicit "Dark" or "Light") they will not see color changes upon enabling OS HCM.
flowchart TD
A[Is OS HCM enabeld?]
A -->|Yes| B[Is FF's theme set to System Auto?]
B --> |Yes| C[Use OS HCM colors to render browser chrome]
B -->|No| D[Use FF theme colors to render browser chrome]
A -->|No| D
Settings that control color usage in content
- Colors Dialog (about:preferences > Contrast Control)
- Extensions like Dark Reader, or changes to user.css, may override author specified colors independent of HCM.
flowchart TD
A[Which option is selected in 'Contrast Control'?]
A -->|Use platform's contrast settings| B[Is a OS HCM enabled?]
A -->|Off| H
A --->|On| I[Use colors dialog colors to render all content (HCM)]
B -->|Yes| C[Use OS colors to render all content (HCM)]
B -->|No| H[Use system colors for all unstyled content]