diff --git a/lib/core/engine/index.js b/lib/core/engine/index.js
index 64c927b64..cec75ba8c 100644
--- a/lib/core/engine/index.js
+++ b/lib/core/engine/index.js
@@ -386,12 +386,34 @@ export class Engine {
         result.info.browser.name = extras.har.log.browser.name;
         result.info.browser.version = extras.har.log.browser.version;
         if (options.browser === 'firefox' && options.firefox) {
-          result.info.browser.args = options.firefox.args;
+          // Issue #1622 — surface the full set of args/preferences/binary
+          // that browsertime applied to Firefox, not just what the user
+          // passed via --firefox.args / --firefox.preference. Captured by
+          // configureBuilder; see lib/firefox/webdriver/builder.js.
+          if (options.recordedBrowserSettings) {
+            const recorded = options.recordedBrowserSettings;
+            result.info.browser.args = recorded.args;
+            result.info.browser.preferences = recorded.preferences;
+            if (recorded.binary) {
+              result.info.browser.binary = recorded.binary;
+            }
+            if (recorded.profile) {
+              result.info.browser.profile = recorded.profile;
+            }
+            if (recorded.androidPackage) {
+              result.info.browser.androidPackage = recorded.androidPackage;
+            }
+            if (recorded.androidActivity) {
+              result.info.browser.androidActivity = recorded.androidActivity;
+            }
+          } else {
+            result.info.browser.args = options.firefox.args;
+            result.info.browser.preference = options.firefox.preference;
+          }
           if (options.firefox.geckoProfiler === true) {
             result.info.browser.geckProfilerFeatures =
               options.firefox.geckoProfilerParams.features;
           }
-          result.info.browser.preference = options.firefox.preference;
         } else if (options.browser === 'chrome') {
           if (options.chrome) {
             result.info.browser.args = options.chrome.args;
diff --git a/lib/core/engine/iteration.js b/lib/core/engine/iteration.js
index c343ca09a..c09f2f15c 100644
--- a/lib/core/engine/iteration.js
+++ b/lib/core/engine/iteration.js
@@ -224,6 +224,14 @@ export class Iteration {
 
     await engineDelegate.beforeBrowserStart();
     await browser.start();
+    // The runner deep-merges options into a fresh object before passing them
+    // to the browser-specific builder, so anything the builder records there
+    // never reaches the engine. Copy it back to the engine's options object
+    // so result.info.browser can pick it up. Issue #1622.
+    if (browser.options && browser.options.recordedBrowserSettings) {
+      this.options.recordedBrowserSettings =
+        browser.options.recordedBrowserSettings;
+    }
     await engineDelegate.afterBrowserStart(browser);
   }
 
diff --git a/lib/firefox/webdriver/builder.js b/lib/firefox/webdriver/builder.js
index 337c7b591..f437f4050 100644
--- a/lib/firefox/webdriver/builder.js
+++ b/lib/firefox/webdriver/builder.js
@@ -266,4 +266,18 @@ export async function configureBuilder(builder, baseDir, options) {
   }
 
   builder.setFirefoxOptions(ffOptions);
+
+  // Snapshot every argument / preference / capability we just applied so it
+  // can be surfaced in the result JSON for debugging — issue #1622. The
+  // runner deep-merges options into a fresh container before this is called,
+  // so iteration.js threads it back to the engine after browser.start().
+  const ffInternals = ffOptions.firefoxOptions_();
+  options.recordedBrowserSettings = {
+    args: [...(ffInternals.args || [])],
+    preferences: { ...ffInternals.prefs },
+    binary: ffInternals.binary,
+    profile: ffInternals.profile,
+    androidPackage: ffInternals.androidPackage,
+    androidActivity: ffInternals.androidActivity
+  };
 }