browser.firefox only api

browser.firefox-only-api

Rule ID: browser.firefox-only-api Severity: WARN Category: browser Target Standards: W3C Fullscreen API Specification, W3C DOM Standards (Gecko Extension Deprecations), MDN Web Docs (Gecko-Specific DOM Interfaces)

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1. Overview & Core Invariant

Flags usage of legacy Gecko/Firefox-exclusive DOM extensions and APIs without standard W3C equivalents

Core Invariant:

"Gecko-prefixed DOM methods and proprietary APIs ('mozRequestFullScreen', 'InstallTrigger', etc.) must provide standard W3C equivalents for Blink and WebKit."

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2. Technical Grounding & Engine Realities

Mozilla Firefox historically exposed vendor-prefixed APIs such as 'mozRequestFullScreen' and browser-specific globals like 'InstallTrigger'.

Calling these directly without standard W3C methods causes instant crashes or undefined behavior in Blink (Chrome/Edge) and WebKit (Safari).

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3. Vulnerability & Risk Taxonomy

Risk Vector	Severity	Impact
Crash in Chrome and Safari	MEDIUM	Invoking 'element.mozRequestFullScreen()' throws 'TypeError: element.mozRequestFullScreen is not a function' in all non-Gecko browsers.
Obsolete Browser Sniffing	LOW	Relying on 'InstallTrigger' to detect Firefox is deprecated and breaks as Firefox modernizes its engine.

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4. Non-Compliant Code Patterns (Bad Examples)

JAVASCRIPT (Direct invocation of mozRequestFullScreen without standard check):

function enterFullscreen(element) {
  element.mozRequestFullScreen();
}

JAVASCRIPT (Direct access to Gecko-specific inner screen property):

const screenX = window.mozInnerScreenX;

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5. Compliant Implementation Patterns (Good Examples)

JAVASCRIPT (Prioritizing standard W3C fullscreen method):

function enterFullscreen(element) {
  if (element.requestFullscreen) {
    element.requestFullscreen();
  } else if (element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  }
}

JAVASCRIPT (Standard fullscreenElement fallback chain):

const fsElement = document.fullscreenElement || document.mozFullScreenElement;

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6. Detection & Verification Pipeline (How The Rule Evaluates Code)

This rule evaluates source code through the standard AST inspection pipeline:

flowchart TD
    Node["AST Node (Astro / TSX element)"] --> Inspect["1. Inspect Element & Attributes"]
    Inspect --> Invariant{"2. Evaluate Rule Invariant"}
    Invariant -- "Compliant" --> Safe["Pass"]
    Invariant -- "Non-Compliant" --> IgnoreCheck{"3. Check charites:ignore directive"}
    IgnoreCheck -- "Ignored" --> Safe
    IgnoreCheck -- "Not Ignored" --> Diag["4. Emit Diagnostic: browser.firefox-only-api"]

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Step-by-Step Evaluation:

1. AST Traversal: Visits normalized ir.Node structures during AST streaming.
2. Invariant Check: Compares node attributes against rule invariants.
3. Directive Suppression Check: Honors inline charites:ignore browser.firefox-only-api directives.
4. Diagnostic Emission: Emits compiler-grade diagnostic on invariant violation.

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7. Verification & Test Harness (How The Test Works: 1-SSOT Tri-Corpus)

This rule is rigorously tested and validated across the canonical 1-SSOT Tri-Corpus in tests/correctness/browser.firefox-only-api/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for browser.firefox-only-api"]
        subgraph P ["Positive Corpus (tests/correctness/browser.firefox-only-api/positive/)"]
            P1["P1: Obvious Direct Violation"]
            P2["P2: Indirect / Variant Concatenation"]
            P3["P3: Helper / clsx / cn Wrapper"]
            P4["P4: Deeply Nested Elements"]
            P5["P5: Aliased Imports / Re-exports"]
        end
        subgraph N ["Negative Corpus (tests/correctness/browser.firefox-only-api/negative/)"]
            N1["N1: Valid Design Tokens"]
            N2["N2: Explicit charites:ignore Directive"]
            N3["N3: Third-Party / Vendor Components"]
            N4["N4: Clean Semantic HTML"]
            N5["N5: Untokenized Custom Values (Banana Test)"]
        end
        subgraph A ["Adversarial Corpus (tests/correctness/browser.firefox-only-api/adversarial/)"]
            A1["A1: Template Literal Interpolations"]
            A2["A2: Ternary Conditional Expressions"]
            A3["A3: Spread Properties & Dynamic Overrides"]
            A4["A4: Dynamic Object Class Syntax"]
            A5["A5: Shadowed Variable Identifiers"]
            A6["A6: Nested Closures & HOC Wrappers"]
            A7["A7: Obfuscated Classes & Cyclic Tokens"]
        end
    end

    P --> TestRunner["Automated Runner (rule_test.go)"]
    N --> TestRunner
    A --> TestRunner
    TestRunner --> Gates["Quality Gates: Zero Panic, Zero False-Positive, Zero Bypass"]

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• Positive Fixtures (P1-P5): Verified to trigger diagnostics at exact lines and column spans.
• Negative Fixtures (N1-N5): Verified to produce zero diagnostics on valid tokens and legitimate exemptions.
• Adversarial Fixtures (A1-A7): Verified to prevent evasion across dynamic expressions, string interpolations, and cyclic references.

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8. How to Suppress (Ignore Directives)

If this pattern is required for an intentional exception, suppress the diagnostic using the canonical Charites Rule ID:

<!-- charites:ignore browser.firefox-only-api intentional exception -->

// charites:ignore browser.firefox-only-api intentional exception

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9. Configuration Reference (charites.yaml)

rules:
  browser.firefox-only-api:
    severity: warn # error | warn | info | off