use chrome.contextMenus instead of browser.menus

this should make the extension fully functional for all mv2 firefox 
versions (since 48)

tested and working in older esr edition.

v0.2.0

README.md

@@ -9,6 +9,8 @@ Supports MD5, SHA; using [crypto-api](https://github.com/nf404/crypto-api)
 #### _Caveat emptor_
   - Hashes of selected multi-line text will differ between Windows and macOS/Linux hosts, because of text line-ending encoding. This is not a bug _per se_, something to be aware of.
   - Doesn't work on `raw.githubusercontent.com` page text. ([Bug](https://bugzilla.mozilla.org/show_bug.cgi?id=1411641))
+
+  - Older versions of Firefox may strip whitespace from the edge of selected text. The hash and text displayed is still correct but doesn't correspond exactly to the selected text with whitespace included.
 
 #### Privacy policy
 

src/background.js

@@ -18,31 +18,31 @@ function onError(error) {
   console.log(`Error: ${error}`);
 }
 
-browser.menus.create({
+chrome.contextMenus.create({
   id: "MD5",
   title: browser.i18n.getMessage("MD5"),
   contexts: ["all"]
 }, onCreated);
 
-browser.menus.create({
+chrome.contextMenus.create({
   id: "separator0",
   type: "separator",
   contexts: ["all"]
 }, onCreated);
 
-browser.menus.create({
+chrome.contextMenus.create({
   id: "SHA1",
   title: browser.i18n.getMessage("SHA1"),
   contexts: ["all"]
 }, onCreated);
 
-browser.menus.create({
+chrome.contextMenus.create({
   id: "SHA256",
   title: browser.i18n.getMessage("SHA256"),
   contexts: ["all"]
 }, onCreated);
 
-browser.menus.create({
+chrome.contextMenus.create({
   id: "SHA512",
   title: browser.i18n.getMessage("SHA512"),
   contexts: ["all"]
@@ -53,7 +53,7 @@ browser.menus.create({
 The click event listener, where we perform the appropriate action given the
 ID of the menu item that was clicked.
 */
-browser.menus.onClicked.addListener((info, tab) => {
+chrome.contextMenus.onClicked.addListener((info, tab) => {
   hash = null;
   hashType = info.menuItemId;
   //console.log(info.selectionText);

src/manifest.json

@@ -4,13 +4,13 @@
   "description": "Hash selected text and pages in the browser.",
   "homepage_url": "https://github.com/wesinator/hashzilla",
   "default_locale": "en",
-  "version": "0.1.6",
+  "version": "0.2.0",
   "icons": {
     "64": "icons/icon.png"
   },
 
   "permissions": [
-    "menus",
+    "contextMenus",
     "activeTab"
   ],