diff --git a/calendar/base/content/calendar-task-editing.js b/calendar/base/content/calendar-task-editing.js
index 3c859544413..f9222d2db43 100644
--- a/calendar/base/content/calendar-task-editing.js
+++ b/calendar/base/content/calendar-task-editing.js
@@ -38,8 +38,36 @@
 /**
  * Used by the "quick add" feature for tasks, for example in the task view or
  * the uniinder-todo.
+ *
+ * NOTE: many of the following methods are called without taskEdit being the
+ * |this| object.
  */
+
 var taskEdit = {
+    mObservedCalendar: null,
+    get observedCalendar tE_get_observedCalendar() {
+        return this.mObservedCalendar;
+    },
+
+    set observedCalendar tE_set_observedCalendar(v) {
+        if (this.mObservedCalendar) {
+            this.mObservedCalendar.removeObserver(this.calendarObserver);
+        }
+
+        this.mObservedCalendar = v;
+
+        if (this.mObservedCalendar) {
+            this.mObservedCalendar.addObserver(this.calendarObserver);
+        }
+        return this.mObservedCalendar;
+    },
+
+    setupTaskField: function tE_setupTaskField(aTarget, aDisable, aValue) {
+        aTarget.value = aValue;
+        setElementValue(aTarget, aDisable && "true", "readonly");
+        setElementValue(aTarget, aDisable && "true", "aria-disabled");
+    },
+
     onFocus: function tE_onFocus(aEvent) {
         var edit = aEvent.target;
         if (edit.localName == "input") {
@@ -47,13 +75,18 @@ var taskEdit = {
             // when debugging with venkman.
             edit = edit.parentNode.parentNode;
         }
-        if (!edit.savedInstructions) {
-            edit.savedInstructions = edit.getAttribute("instructions");
+
+        var calendar = getSelectedCalendar();
+
+        if (calendar.getProperty("capabilities.tasks.supported") === false) {
+            taskEdit.setupTaskField(edit, true, calGetString("calendar", "taskEditInstructionsCapability"));
+        } else if (!isCalendarWritable(calendar)) {
+            taskEdit.setupTaskField(edit, true, calGetString("calendar", "taskEditInstructionsReadonly"));
+        } else {
+            taskEdit.setupTaskField(edit, false, edit.savedValue || "");
         }
-        edit.value = edit.savedValue || "";
-        edit.removeAttribute("instructions");
     },
-    
+
     onBlur: function tE_onBlur(aEvent) {
         var edit = aEvent.target;
         if (edit.localName == "input") {
@@ -62,9 +95,17 @@ var taskEdit = {
             // the parent chain until we reach the textbox.
             edit = edit.parentNode.parentNode;
         }
-        edit.savedValue = edit.value;
-        edit.value = edit.savedInstructions;
-        edit.setAttribute("instructions", edit.savedInstructions);
+
+        var calendar = getSelectedCalendar();
+
+        if (calendar.getProperty("capabilities.tasks.supported") === false) {
+            taskEdit.setupTaskField(edit, true, calGetString("calendar", "taskEditInstructionsCapability"));
+        } else if (!isCalendarWritable(getSelectedCalendar())) {
+            taskEdit.setupTaskField(edit, true, calGetString("calendar", "taskEditInstructionsReadonly"));
+        } else {
+            edit.savedValue = edit.value;
+            taskEdit.setupTaskField(edit, false, calGetString("calendar", "taskEditInstructions"));
+        }
     },
 
     onKeyPress: function tE_onKeyPress(aEvent) {
@@ -85,5 +126,81 @@ var taskEdit = {
                 });
             }
         }
+    },
+
+    onLoad: function tE_onLoad(aEvent) {
+        window.removeEventListener("load", taskEdit.onLoad, false);
+        var taskEditFields = document.getElementsByAttribute("class", "task-edit-field");
+        for (var i = 0; i < taskEditFields.length; i++) {
+            taskEdit.onBlur({ target: taskEditFields[i] });
+        }
+
+        getCompositeCalendar().addObserver(taskEdit.compositeObserver);
+        taskEdit.observedCalendar = getSelectedCalendar();
+    },
+
+    onUnload: function tE_onUnload() {
+        getCompositeCalendar().removeObserver(taskEdit.compositeObserver);
+        taskEdit.observedCalendar = null;
+    },
+
+    calendarObserver: {
+        QueryInterface: function tE_QueryInterface(aIID) {
+            return doQueryInterface(this, calendarListTreeView.__proto__, aIID,
+                                    [Components.interfaces.calIObserver]);
+        },
+
+        onPropertyChanged: function tE_calObs_onPropertyChanged(aCalendar,
+                                                         aName,
+                                                         aValue,
+                                                         aOldValue) {
+            if (aCalendar.id != getSelectedCalendar().id) {
+                // Optimization: if the given calendar isn't the default calendar,
+                // then we don't need to change any readonly/disabled states.
+                return;
+            }
+            switch (aName) {
+                case "readOnly":
+                case "disabled":
+                    var taskEditFields = document.getElementsByAttribute("class", "task-edit-field");
+                    for (var i = 0; i < taskEditFields.length; i++) {
+                        taskEdit.onBlur({ target: taskEditFields[i] });
+                    }
+            }
+        },
+
+        onPropertyDeleting: function tE_calObs_onPropertyDeleting(aCalendar,
+                                                           aName) {
+            // Since the old value is not used directly in onPropertyChanged,
+            // but should not be the same as the value, set it to a different
+            // value.
+            this.onPropertyChanged(aCalendar, aName, null, null);
+        },
+
+        __noSuchMethod__: function tE_calObs___noSuchMethod__(aMethod, aArgs) {
+            // Swallow other methods that don't need to be implemented
+        }
+    },
+
+    compositeObserver: {
+        QueryInterface: function tE_QueryInterface(aIID) {
+            return doQueryInterface(this, calendarListTreeView.__proto__, aIID,
+                                    [Components.interfaces.calIObserver,
+                                     Components.interfaces.calICompositeObserver]);
+        },
+
+        onDefaultCalendarChanged: function tE_compObs_onDefaultCalendarChanged(aNewDefault) {
+            var taskEditFields = document.getElementsByAttribute("class", "task-edit-field");
+            for (var i = 0; i < taskEditFields.length; i++) {
+                taskEdit.onBlur({ target: taskEditFields[i] });
+            }
+            taskEdit.observedCalendar = aNewDefault;
+        },
+        __noSuchMethod__: function tE_compObs___noSuchMethod__(aMethod, aArgs) {
+            // Swallow other methods that don't need to be implemented
+        }
     }
 };
+
+window.addEventListener("load", taskEdit.onLoad, false);
+window.addEventListener("unload", taskEdit.onUnload, false);
diff --git a/calendar/base/content/calendar-task-view.xul b/calendar/base/content/calendar-task-view.xul
index f4b98920ef7..5e3fdfbb61c 100644
--- a/calendar/base/content/calendar-task-view.xul
+++ b/calendar/base/content/calendar-task-view.xul
@@ -57,8 +57,6 @@
           onselect="taskDetailsView.onSelect(event);">
       <textbox id="view-task-edit-field"
                class="task-edit-field"
-               value="&calendar.task.edit.instructions.label;"
-               instructions="&calendar.task.edit.instructions.label;"
                onfocus="taskEdit.onFocus(event)"
                onblur="taskEdit.onBlur(event)"
                onkeypress="taskEdit.onKeyPress(event)"/>
diff --git a/calendar/base/content/calendar-unifinder-todo.xul b/calendar/base/content/calendar-unifinder-todo.xul
index 22b42c21882..b50f3abfa1e 100644
--- a/calendar/base/content/calendar-unifinder-todo.xul
+++ b/calendar/base/content/calendar-unifinder-todo.xul
@@ -74,8 +74,6 @@
       <textbox id="unifinder-task-edit-field"
                class="task-edit-field"
                flex="1"
-               value="&calendar.task.edit.instructions.label;"
-               instructions="&calendar.task.edit.instructions.label;"
                onfocus="taskEdit.onFocus(event)"
                onblur="taskEdit.onBlur(event)"
                onkeypress="taskEdit.onKeyPress(event)"/>
diff --git a/calendar/base/themes/pinstripe/calendar-task-view.css b/calendar/base/themes/pinstripe/calendar-task-view.css
index ebaff3d2a03..209fe2cbb6e 100644
--- a/calendar/base/themes/pinstripe/calendar-task-view.css
+++ b/calendar/base/themes/pinstripe/calendar-task-view.css
@@ -61,8 +61,8 @@
     margin: 5px;
 }
 
-.task-edit-field[instructions] {
-    color: grey;
+.task-edit-field[readonly="true"] {
+    color: GrayText;
 }
 
 .task-quickadd-box {
diff --git a/calendar/base/themes/winstripe/calendar-task-view.css b/calendar/base/themes/winstripe/calendar-task-view.css
index 1c44240073c..7daa7fb9f39 100644
--- a/calendar/base/themes/winstripe/calendar-task-view.css
+++ b/calendar/base/themes/winstripe/calendar-task-view.css
@@ -65,8 +65,8 @@
     margin: 5px;
 }
 
-.task-edit-field[instructions] {
-    color: grey;
+.task-edit-field[readonly="true"] {
+    color: GrayText;
 }
 
 .task-quickadd-box {
diff --git a/calendar/locales/en-US/chrome/calendar/calendar.dtd b/calendar/locales/en-US/chrome/calendar/calendar.dtd
index 8b2c265d1d7..812edc2c32b 100644
--- a/calendar/locales/en-US/chrome/calendar/calendar.dtd
+++ b/calendar/locales/en-US/chrome/calendar/calendar.dtd
@@ -196,7 +196,6 @@
 <!ENTITY calendar.task.filter.completed.label       "Completed Tasks">
 <!ENTITY calendar.task.filter.completed.accesskey   "C">
 
-<!ENTITY calendar.task.edit.instructions.label       "Click Here to Add a New Task">
 <!ENTITY calendar.task.details.title.label           "Title:">
 <!ENTITY calendar.task.details.entrydate.label       "Start Date:">
 <!ENTITY calendar.task.details.duedate.label         "Due Date:">
diff --git a/calendar/locales/en-US/chrome/calendar/calendar.properties b/calendar/locales/en-US/chrome/calendar/calendar.properties
index fd00c9c2e20..7d66a8a7876 100644
--- a/calendar/locales/en-US/chrome/calendar/calendar.properties
+++ b/calendar/locales/en-US/chrome/calendar/calendar.properties
@@ -332,3 +332,7 @@ taskDetailsStatusCancelled=Cancelled
 
 gettingCalendarInfoCommon=Checking Calendars\u2026
 gettingCalendarInfoDetail=Checking Calendar %1$S of %2$S
+
+taskEditInstructions=Click Here to Add a New Task
+taskEditInstructionsReadonly=Please Select a Writable Calendar
+taskEditInstructionsCapability=Please Select a Calendar that Supports Tasks
diff --git a/calendar/providers/composite/calCompositeCalendar.js b/calendar/providers/composite/calCompositeCalendar.js
index 33484f027f6..721a1b5f4d3 100644
--- a/calendar/providers/composite/calCompositeCalendar.js
+++ b/calendar/providers/composite/calCompositeCalendar.js
@@ -250,11 +250,8 @@ calCompositeCalendar.prototype = {
     },
 
     setDefaultCalendar: function (cal, usePref) {
-        // Don't do anything if the passed calendar is the default calendar, or
-        // the passed calendar is disabled.
-        if (cal &&
-            ((this.mDefaultCalendar && this.mDefaultCalendar.id == cal.id) ||
-             cal.getProperty("disabled"))) {
+        // Don't do anything if the passed calendar is the default calendar
+        if (cal && this.mDefaultCalendar && this.mDefaultCalendar.id == cal.id) {
             return;
         }
         if (usePref && this.mPrefPrefix) {