Starting to get the hang out of it. I can detect clicks on save now. Next step is to try to save data.

fortNoxOvertime/fortnox.js

@@ -0,0 +1,39 @@
+
+
+////////////////////////////////
+/**
+ * OverTime calculation related code
+ */
+////////////////////////////////
+
+/*
+* Checks whether our browser supports LocalStorage
+*/
+function supports_html5_storage() {
+  try {
+    return 'localStorage' in window && window['localStorage'] !== null;
+  } catch (e) {
+    return false;
+  }
+}
+
+//Main action
+// We want to operate only on the right page, and if localStorage can be used
+if (document.title.indexOf("Fortnox") != -1 && supports_html5_storage()) {
+    //Creating Elements
+    var btn = document.createElement("BUTTON")
+    var t = document.createTextNode("CLICK ME");
+    btn.appendChild(t);
+    //Appending to DOMo
+    document.body.appendChild(btn);
+
+    document.getElementById("button_save_and_group").onclick= function(event) {
+        alert("caca");
+    // Compensate for IE<9's non-standard event model
+    //
+        if (event===undefined) event= window.event;
+        var target= 'target' in event? event.target : event.srcElement;
+
+        alert('clicked on '+target.tagName);
+    };
+}

fortNoxOvertime/getHours.js

@@ -0,0 +1,115 @@
+var weeklyHours = 40; // Number of hours to be worked per week
+
+/*
+* Checks whether our browser supports LocalStorage
+*/
+function supports_html5_storage() {
+  try {
+    return 'localStorage' in window && window['localStorage'] !== null;
+  } catch (e) {
+    return false;
+  }
+}
+
+/*
+* The method that is run instead of deliver.
+* Contains all the statistics calculation
+*/
+function saveStatistics(){
+
+    var workingTime = calculateWorkingTime();
+    var overtime = calculateOvertime(workingTime);
+
+    console.log("Overtime this week : " + overtime);
+
+    // Need to store the information somewhere now. Using localStorage
+    saveWorkingTime(workingTime);
+    saveWeekOvertime(overtime);
+    saveOvertime(overtime);
+
+    //Giving original behaviour back
+    SaveWeekRows(true);
+}
+
+/*
+* Calculate the amount of hours worked this week
+*/
+function calculateWorkingTime(){
+    var hours = parseInt(document.getElementById("info_hour_sum").innerHTML);
+    return hours;
+}
+
+/*
+* Calculates the number of extra hours I worked this week
+*/
+function calculateOvertime(workingTime){
+    var weeklyOvertime = workingTime - weeklyHours;
+
+    if(weeklyOvertime > 0){
+      return weeklyOvertime;
+    }
+    else{
+      return 0;
+    }
+}
+
+function saveOvertime(overtime){
+    key = "overtime";
+    var current = localStorage[key];
+
+    // Checking for possible problems
+    if(isNaN(current)){
+      current = 0;
+    }
+
+    localStorage[key] = current + overtime;
+}
+
+/*
+* Saves the total time worked for a given week
+* The key used is the fortnox code for this week  :
+* year + weeknumber + month : 1409-02 for 9th week of 2014 in february + over
+*/
+function saveWorkingTime(workingTime){
+
+  var weekKey = getWeekKey();
+  localStorage[weekKey] = workingTime;
+}
+
+/*
+* Saves the overtime for a given week
+* The key used is the fortnox code for this week  :
+* year + weeknumber + month : 1409-02 for 9th week of 2014 in february
+*/
+function saveWeekOvertime(overtime){
+  var weekOvertimeKey = getWeekOvertimeKey();
+  localStorage[weekOvertimeKey] = overtime;
+}
+
+/*
+* creates a hash key for the weekly working time
+*/
+function getWeekKey(){
+  return document.getElementById("time_week").value;
+}
+
+/*
+* creates a hash key for the weekly overtime
+*/
+function getWeekOvertimeKey(){
+  return getWeekKey() + "_overtime";
+}
+
+
+/*
+Happens no matter what
+*/
+var ok = supports_html5_storage();
+if(ok){
+    alert("Local Storage allowed!");
+}
+else{
+  alert("Your browser does not support LocalStorage!");
+}
+
+document.getElementById("button_save_and_group").onclick = saveStatistics;

fortNoxOvertime/manifest.json

@@ -4,12 +4,11 @@
   "name": "FortNox Overtime",
   "description": "This extension keeps track of my days off and overtime in FortNox",
   "version": "1.0",
-
-  "permissions": [
-    "https://secure.flickr.com/"
-  ],
-  "browser_action": {
-    "default_icon": "icon.png",
-    "default_popup": "popup.html"
-  }
+  "content_scripts": [
+      {
+        "matches": ["https://apps2.fortnox.se/time/time_time/*"],
+        "js": ["fortnox.js"]
+      }
+    ]
+  // "web_accessible_resources": ["getHours.js"]
 }