new file mode 100644
--- /dev/null
+++ b/testing/marionette/doc/internals/log.rst
@@ -0,0 +1,4 @@
+log module
+==========
+.. js:autoclass:: Log
+  :members:

--- a/testing/marionette/jar.mn
+++ b/testing/marionette/jar.mn
@@ -19,16 +19,17 @@ marionette.jar:
   content/error.js (error.js)
   content/evaluate.js (evaluate.js)
   content/event.js  (event.js)
   content/format.js (format.js)
   content/interaction.js (interaction.js)
   content/l10n.js (l10n.js)
   content/legacyaction.js (legacyaction.js)
   content/listener.js (listener.js)
+  content/log.js (log.js)
   content/message.js (message.js)
   content/modal.js (modal.js)
   content/navigate.js (navigate.js)
   content/packets.js (packets.js)
   content/prefs.js (prefs.js)
   content/proxy.js (proxy.js)
   content/reftest.js (reftest.js)
   content/reftest.xul (reftest.xul)

new file mode 100644
--- /dev/null
+++ b/testing/marionette/log.js
@@ -0,0 +1,94 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+ChromeUtils.import("resource://gre/modules/Services.jsm");
+const StdLog = ChromeUtils.import("resource://gre/modules/Log.jsm", {}).Log;
+
+const {MarionettePrefs} = ChromeUtils.import("chrome://marionette/content/prefs.js", {});
+
+this.EXPORTED_SYMBOLS = ["Log"];
+
+const isChildProcess = Services.appinfo.processType ==
+    Services.appinfo.PROCESS_TYPE_CONTENT;
+
+/**
+ * Shorthand for accessing the Marionette logging repository.
+ *
+ * Using this class to retrieve the `Log.jsm` repository for
+ * Marionette will ensure the logger is set up correctly with the
+ * appropriate stdout dumper and with the correct log level.
+ *
+ * Unlike `Log.jsm` this logger is E10s safe, meaning repository
+ * configuration for appenders and logging levels are communicated
+ * across processes.
+ *
+ * @name Log
+ */
+class MarionetteLog {
+  /**
+   * Obtain the `Marionette` logger.
+   *
+   * The returned {@link Logger} instance is shared among all
+   * callers in the same process.
+   *
+   * @return {Logger}
+   */
+  static get() {
+    let logger = StdLog.repository.getLogger("Marionette");
+    if (logger.ownAppenders.length == 0) {
+      logger.addAppender(new StdLog.DumpAppender());
+    }
+    logger.level = MarionettePrefs.logLevel;
+    return logger;
+  }
+
+  /**
+   * Obtain a logger that logs all messages with a prefix.
+   *
+   * Unlike {@link LoggerRepository.getLoggerWithMessagePrefix()}
+   * this function will ensure invoke {@link #get()} first to ensure
+   * the logger has been properly set up first.
+   *
+   * This returns a new object with a prototype chain that chains
+   * up the original {@link Logger} instance.  The new prototype has
+   * log functions that prefix `prefix` to each message.
+   *
+   * @param {string} prefix
+   *     String to prefix each logged message with.
+   *
+   * @return {Proxy.<Logger>}
+   */
+  static getWithPrefix(prefix) {
+    this.get();
+    return StdLog.repository.getLoggerWithMessagePrefix("Marionette", `[${prefix}] `);
+  }
+}
+
+class ParentProcessLog extends MarionetteLog {
+  static get() {
+    let logger = super.get();
+    Services.ppmm.initialProcessData["Marionette:Log"] = {level: logger.level};
+    return logger;
+  }
+}
+
+class ChildProcessLog extends MarionetteLog {
+  static get() {
+    let logger = super.get();
+
+    // Log.jsm is not e10s compatible (see https://bugzil.la/1411513)
+    // so loading it in a new child process will reset the repository config
+    logger.level = Services.cpmm.initialProcessData["Marionette:Log"] || StdLog.Level.Info;
+
+    return logger;
+  }
+}
+
+if (isChildProcess) {
+  this.Log = ChildProcessLog;
+} else {
+  this.Log = ParentProcessLog;
+}

--- a/testing/marionette/prefs.js
+++ b/testing/marionette/prefs.js
@@ -121,24 +121,16 @@ class Branch {
  * potentially malformed input.  In the `marionette.log.level` example,
  * `DEBUG`, `Debug`, and `dEbUg` are considered valid inputs and the
  * `LogBranch` specialisation deserialises the string value to the
  * correct `Log.Level` by sanitising the input data first.
  *
  * A further complication is that we cannot rely on `Preferences.jsm`
  * in Marionette.  See https://bugzilla.mozilla.org/show_bug.cgi?id=1357517
  * for further details.
- *
- * Usage::
- *
- *     ChromeUtils.import("resource://gre/modules/Log.jsm");
- *     const {MarionettePrefs} = ChromeUtils.import("chrome://marionette/content/prefs.js", {});
- *
- *     const log = Log.repository.getLogger("Marionette");
- *     log.level = MarionettePrefs.log.level;
  */
 class MarionetteBranch extends Branch {
   constructor(branch = "marionette.") {
     super(branch);
   }
 
   /**
    * The `marionette.enabled` preference.  When it returns true,