--- a/browser/modules/Sanitizer.jsm
+++ b/browser/modules/Sanitizer.jsm
@@ -270,16 +270,20 @@ var Sanitizer = {
     }
   },
 
   QueryInterface: XPCOMUtils.generateQI([
     Ci.nsiObserver,
     Ci.nsISupportsWeakReference
   ]),
 
+  // When making any changes to the sanitize implementations here,
+  // please check whether the changes are applicable to Android
+  // (mobile/android/modules/Sanitizer.jsm) as well.
+
   items: {
     cache: {
       async clear(range) {
         let seenException;
         let refObj = {};
         TelemetryStopwatch.start("FX_SANITIZE_CACHE", refObj);
 
         try {

--- a/mobile/android/modules/Sanitizer.jsm
+++ b/mobile/android/modules/Sanitizer.jsm
@@ -62,17 +62,26 @@ Sanitizer.prototype = {
         }
       };
       return maybeDoClear();
     } else if (canClear) {
       return item.clear(options);
     }
   },
 
+  // This code is mostly based on the Sanitizer code for desktop Firefox
+  // (browser/modules/Sanitzer.jsm), however over the course of time some
+  // general differences have evolved:
+  // - async shutdown (and seenException handling) isn't implemented in Fennec
+  // - currently there is only limited support for range-based clearing of data
+
+  // Any further specific differences caused by architectural differences between
+  // Fennec and desktop Firefox are documented below for each item.
   items: {
+    // Same as desktop Firefox.
     cache: {
       clear: function() {
         return new Promise(function(resolve, reject) {
           let refObj = {};
           TelemetryStopwatch.start("FX_SANITIZE_CACHE", refObj);
 
           try {
             Services.cache2.clear();
@@ -89,16 +98,18 @@ Sanitizer.prototype = {
         });
       },
 
       get canClear() {
         return true;
       }
     },
 
+    // Compared to desktop, we don't clear plugin data, as plugins
+    // aren't supported on Android.
     cookies: {
       clear: function() {
         return new Promise(function(resolve, reject) {
           let refObj = {};
           TelemetryStopwatch.start("FX_SANITIZE_COOKIES_2", refObj);
 
           Services.cookies.removeAll();
 
@@ -115,16 +126,17 @@ Sanitizer.prototype = {
         });
       },
 
       get canClear() {
         return true;
       }
     },
 
+    // Same as desktop Firefox.
     siteSettings: {
       clear: Task.async(function* () {
         let refObj = {};
         TelemetryStopwatch.start("FX_SANITIZE_SITESETTINGS", refObj);
 
         // Clear site-specific permissions like "Allow this site to open popups"
         Services.perms.removeAll();
 
@@ -154,16 +166,17 @@ Sanitizer.prototype = {
         TelemetryStopwatch.finish("FX_SANITIZE_SITESETTINGS", refObj);
       }),
 
       get canClear() {
         return true;
       }
     },
 
+    // Same as desktop Firefox.
     offlineApps: {
       async clear() {
         // AppCache
         // This doesn't wait for the cleanup to be complete.
         OfflineAppCacheHelper.clear();
 
         // LocalStorage
         Services.obs.notifyObservers(null, "extension:purge-localStorage");
@@ -199,16 +212,18 @@ Sanitizer.prototype = {
         return Promise.all(promises);
       },
 
       get canClear() {
           return true;
       }
     },
 
+    // History on Android is implemented by the Java frontend and requires
+    // different handling. Everything else is the same as for desktop Firefox.
     history: {
       clear: function() {
         let refObj = {};
         TelemetryStopwatch.start("FX_SANITIZE_HISTORY", refObj);
 
         return EventDispatcher.instance.sendRequestForResult({ type: "Sanitize:ClearHistory" })
           .catch(e => Cu.reportError("Java-side history clearing failed: " + e))
           .then(function() {
@@ -226,16 +241,18 @@ Sanitizer.prototype = {
 
       get canClear() {
         // bug 347231: Always allow clearing history due to dependencies on
         // the browser:purge-session-history notification. (like error console)
         return true;
       }
     },
 
+    // Equivalent to openWindows on desktop, but specific to Fennec's implementation
+    // of tabbed browsing and the session store.
     openTabs: {
       clear: function() {
         let refObj = {};
         TelemetryStopwatch.start("FX_SANITIZE_OPENWINDOWS", refObj);
 
         return EventDispatcher.instance.sendRequestForResult({ type: "Sanitize:OpenTabs" })
           .catch(e => Cu.reportError("Java-side tab clearing failed: " + e))
           .then(function() {
@@ -247,27 +264,30 @@ Sanitizer.prototype = {
           });
       },
 
       get canClear() {
         return true;
       }
     },
 
+    // Specific to Fennec.
     searchHistory: {
       clear: function() {
         return EventDispatcher.instance.sendRequestForResult({ type: "Sanitize:ClearHistory", clearSearchHistory: true })
           .catch(e => Cu.reportError("Java-side search history clearing failed: " + e));
       },
 
       get canClear() {
         return true;
       }
     },
 
+    // Browser search is handled by searchHistory above and the find bar doesn't
+    // require extra handling. FormHistory itself is cleared like on desktop.
     formdata: {
       clear: function({ startTime = 0 } = {}) {
         return new Promise(function(resolve, reject) {
           let refObj = {};
           TelemetryStopwatch.start("FX_SANITIZE_FORMDATA", refObj);
 
           // Conver time to microseconds
           let time = startTime * 1000;
@@ -289,16 +309,17 @@ Sanitizer.prototype = {
           handleResult: function(aResult) { count = aResult; },
           handleError: function(aError) { Cu.reportError(aError); },
           handleCompletion: function(aReason) { aCallback(aReason == 0 && count > 0); }
         };
         FormHistory.count({}, countDone);
       }
     },
 
+    // Adapted from desktop, but heavily modified - see comments below.
     downloadFiles: {
       clear: Task.async(function* ({ startTime = 0, deleteFiles = true} = {}) {
         let refObj = {};
         TelemetryStopwatch.start("FX_SANITIZE_DOWNLOADS", refObj);
 
         let list = yield Downloads.getList(Downloads.ALL);
         let downloads = yield list.getAll();
         var finalizePromises = [];
@@ -338,30 +359,32 @@ Sanitizer.prototype = {
         TelemetryStopwatch.finish("FX_SANITIZE_DOWNLOADS", refObj);
       }),
 
       get canClear() {
         return true;
       }
     },
 
+    // Specific to Fennec.
     passwords: {
       clear: function() {
         return new Promise(function(resolve, reject) {
           Services.logins.removeAllLogins();
           resolve();
         });
       },
 
       get canClear() {
         let count = Services.logins.countLogins("", "", ""); // count all logins
         return (count > 0);
       }
     },
 
+    // Same as desktop Firefox.
     sessions: {
       clear: function() {
         return new Promise(function(resolve, reject) {
           let refObj = {};
           TelemetryStopwatch.start("FX_SANITIZE_SESSIONS", refObj);
 
           // clear all auth tokens
           var sdr = Cc["@mozilla.org/security/sdr;1"].getService(Ci.nsISecretDecoderRing);
@@ -375,16 +398,17 @@ Sanitizer.prototype = {
         });
       },
 
       get canClear() {
         return true;
       }
     },
 
+    // Specific to Fennec.
     syncedTabs: {
       clear: function() {
         return EventDispatcher.instance.sendRequestForResult({ type: "Sanitize:ClearSyncedTabs" })
           .catch(e => Cu.reportError("Java-side synced tabs clearing failed: " + e));
       },
 
       canClear: function(aCallback) {
         Accounts.anySyncAccountsExist().then(aCallback)