Add cross-platform visual test tolerance for CI

Font rendering differs between macOS (Core Text) and Linux (FreeType),
causing ~2% pixel mismatch in Firefox visual tests. Allow 2.5% tolerance
in CI only; local tests remain exact match (0%).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: richardkmichael

tests/firefox/extension.spec.js

@@ -468,6 +468,10 @@ describe('Navigation', function () {
 // Dynamic content is frozen after loading for deterministic baselines.
 // ============================================================
 
+// Cross-platform font rendering tolerance: macOS baselines vs Linux in CI.
+// Matches Playwright's maxDiffPixelRatio: 0.02 (2%) for Chrome visual tests.
+const VISUAL_MISMATCH_TOLERANCE = process.env.CI ? 2.5 : 0;
+
 describe('Visual', function () {
   beforeEach(async function () {
     await clearAllStorage();
@@ -496,15 +500,15 @@ describe('Visual', function () {
     });
     await browser.pause(500);
 
-    await expect(browser).toMatchFullPageSnapshot('popup-with-issues');
+    await expect(browser).toMatchFullPageSnapshot('popup-with-issues', VISUAL_MISMATCH_TOLERANCE);
   });
 
   it('popup empty state', async function () {
     await browser.url(popupUrl());
     await $('#empty-state').waitForDisplayed({ timeout: 10000 });
     await browser.pause(300);
 
-    await expect(browser).toMatchFullPageSnapshot('popup-empty');
+    await expect(browser).toMatchFullPageSnapshot('popup-empty', VISUAL_MISMATCH_TOLERANCE);
   });
 
   it('popup import section', async function () {
@@ -515,14 +519,14 @@ describe('Visual', function () {
     await $('#import-section').waitForDisplayed({ timeout: 5000 });
     await browser.pause(300);
 
-    await expect(browser).toMatchFullPageSnapshot('popup-import');
+    await expect(browser).toMatchFullPageSnapshot('popup-import', VISUAL_MISMATCH_TOLERANCE);
   });
 
   it('options default state', async function () {
     await browser.url(optionsUrl());
     await browser.pause(500);
 
-    await expect(browser).toMatchFullPageSnapshot('options-default');
+    await expect(browser).toMatchFullPageSnapshot('options-default', VISUAL_MISMATCH_TOLERANCE);
   });
 
   it('options with token configured', async function () {
@@ -536,6 +540,6 @@ describe('Visual', function () {
     await browser.url(optionsUrl());
     await browser.pause(500);
 
-    await expect(browser).toMatchFullPageSnapshot('options-configured');
+    await expect(browser).toMatchFullPageSnapshot('options-configured', VISUAL_MISMATCH_TOLERANCE);
   });
 });