Added import feature.

src/scripts/background.js

@@ -0,0 +1,23 @@
+document.getElementById("inputId").onchange = (e) => {
+    var reader = new FileReader();
+    reader.onloadend = function(obj){
+        let data       = obj.target.result;
+        let enteryName = prompt("What is this session's name?", "" + new Date().toLocaleString()
+                                                                               .split(',')[0]);
+        if (enteryName) {
+            browser.storage.local.set({[enteryName]: data});
+        }
+    };
+
+    if (e.target.files[0].type == "application/json")
+        reader.readAsText(e.target.files[0], {encoding: "string"});
+};
+
+
+document.addEventListener("click", (e) => {
+    if (e.button == 0) {  // Left click
+        if (e.target.className == "container") {
+            document.getElementById("inputId").click();
+        }
+    }
+});