diff --git a/browser/devtools/webconsole/test/Makefile.in b/browser/devtools/webconsole/test/Makefile.in
index 84cb0cc3303a..2441e4c9daab 100644
--- a/browser/devtools/webconsole/test/Makefile.in
+++ b/browser/devtools/webconsole/test/Makefile.in
@@ -132,6 +132,7 @@ MOCHITEST_BROWSER_FILES = \
 	browser_bug_871156_ctrlw_close_tab.js \
 	browser_console_private_browsing.js \
 	browser_console_nsiconsolemessage.js \
+	browser_webconsole_bug_817834_add_edited_input_to_history.js \
 	head.js \
 	$(NULL)
 
diff --git a/browser/devtools/webconsole/test/browser_webconsole_bug_817834_add_edited_input_to_history.js b/browser/devtools/webconsole/test/browser_webconsole_bug_817834_add_edited_input_to_history.js
new file mode 100644
index 000000000000..2f075a3a4719
--- /dev/null
+++ b/browser/devtools/webconsole/test/browser_webconsole_bug_817834_add_edited_input_to_history.js
@@ -0,0 +1,61 @@
+/* -*- Mode: js2; js2-basic-offset: 2; indent-tabs-mode: nil; -*- */
+/* vim:set ts=2 sw=2 sts=2 et: */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ *
+ * Contributor(s):
+ *  zmgmoz <zmgmoz@gmail.com>
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+// Test that user input that is not submitted in the command line input is not
+// lost after navigating in history.
+// See https://bugzilla.mozilla.org/show_bug.cgi?id=817834
+
+function test() {
+  addTab("data:text/html;charset=utf-8,Web Console test for bug 817834");
+  browser.addEventListener("load", function onLoad() {
+    browser.removeEventListener("load", onLoad, true);
+    openConsole(null, testEditedInputHistory);
+  }, true);
+}
+
+function testEditedInputHistory(HUD) {
+  let jsterm = HUD.jsterm;
+  let inputNode = jsterm.inputNode;
+  ok(!inputNode.value, "inputNode.value is empty");
+  is(inputNode.selectionStart, 0);
+  is(inputNode.selectionEnd, 0);
+
+  jsterm.setInputValue('"first item"');
+  EventUtils.synthesizeKey("VK_UP", {});
+  is(inputNode.value, '"first item"', "null test history up");
+  EventUtils.synthesizeKey("VK_DOWN", {});
+  is(inputNode.value, '"first item"', "null test history down");
+
+  jsterm.execute();
+  is(inputNode.value, "", "cleared input line after submit");
+
+  jsterm.setInputValue('"editing input 1"');
+  EventUtils.synthesizeKey("VK_UP", {});
+  is(inputNode.value, '"first item"', "test history up");
+  EventUtils.synthesizeKey("VK_DOWN", {});
+  is(inputNode.value, '"editing input 1"',
+    "test history down restores in-progress input");
+
+  jsterm.setInputValue('"second item"');
+  jsterm.execute();
+  jsterm.setInputValue('"editing input 2"');
+  EventUtils.synthesizeKey("VK_UP", {});
+  is(inputNode.value, '"second item"', "test history up");
+  EventUtils.synthesizeKey("VK_UP", {});
+  is(inputNode.value, '"first item"', "test history up");
+  EventUtils.synthesizeKey("VK_DOWN", {});
+  is(inputNode.value, '"second item"', "test history down");
+  EventUtils.synthesizeKey("VK_DOWN", {});
+  is(inputNode.value, '"editing input 2"',
+     "test history down restores new in-progress input again");
+
+  executeSoon(finishTest);
+}
diff --git a/browser/devtools/webconsole/webconsole.js b/browser/devtools/webconsole/webconsole.js
index e9bd387068aa..8e6ac70716ad 100644
--- a/browser/devtools/webconsole/webconsole.js
+++ b/browser/devtools/webconsole/webconsole.js
@@ -2683,8 +2683,14 @@ function JSTerm(aWebConsoleFrame)
 
   this.lastCompletion = { value: null };
   this.history = [];
-  this.historyIndex = 0;
-  this.historyPlaceHolder = 0;  // this.history.length;
+
+  // Holds the number of entries in history. This value is incremented in
+  // this.execute().
+  this.historyIndex = 0; // incremented on this.execute()
+
+  // Holds the index of the history entry that the user is currently viewing.
+  // This is reset to this.history.length when this.execute() is invoked.
+  this.historyPlaceHolder = 0;
   this._objectActorsInVariablesViews = new Map();
 
   this._keyPress = this.keyPress.bind(this);
@@ -2954,8 +2960,10 @@ JSTerm.prototype = {
     let options = { frame: this.SELECTED_FRAME };
     this.requestEvaluation(aExecuteString, options).then(onResult, onResult);
 
-    this.history.push(aExecuteString);
-    this.historyIndex++;
+    // Append a new value in the history of executed code, or overwrite the most
+    // recent entry. The most recent entry may contain the last edited input
+    // value that was not evaluated yet.
+    this.history[this.historyIndex++] = aExecuteString;
     this.historyPlaceHolder = this.history.length;
     this.setInputValue("");
     this.clearCompletion();
@@ -3937,27 +3945,26 @@ JSTerm.prototype = {
       if (this.historyPlaceHolder <= 0) {
         return false;
       }
-
       let inputVal = this.history[--this.historyPlaceHolder];
-      if (inputVal){
-        this.setInputValue(inputVal);
+
+      // Save the current input value as the latest entry in history, only if
+      // the user is already at the last entry.
+      // Note: this code does not store changes to items that are already in
+      // history.
+      if (this.historyPlaceHolder+1 == this.historyIndex) {
+        this.history[this.historyIndex] = this.inputNode.value || "";
       }
+
+      this.setInputValue(inputVal);
     }
     // Down Arrow key
     else if (aDirection == HISTORY_FORWARD) {
-      if (this.historyPlaceHolder == this.history.length - 1) {
-        this.historyPlaceHolder ++;
-        this.setInputValue("");
-      }
-      else if (this.historyPlaceHolder >= (this.history.length)) {
+      if (this.historyPlaceHolder >= (this.history.length-1)) {
         return false;
       }
-      else {
-        let inputVal = this.history[++this.historyPlaceHolder];
-        if (inputVal){
-          this.setInputValue(inputVal);
-        }
-      }
+
+      let inputVal = this.history[++this.historyPlaceHolder];
+      this.setInputValue(inputVal);
     }
     else {
       throw new Error("Invalid argument 0");