diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b4b3a9f2..e7924027 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -30,7 +30,8 @@ opening an issue, read these pointers.
 
 ## Contributing code
 
-- Make sure you have a [GitHub account](https://github.com/join)
+You can find issues to work on by looking at the [help wanted](https://github.com/xtermjs/xterm.js/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22) or [good first issue](https://github.com/xtermjs/xterm.js/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22) issues. It's a good idea to comment on the issue saying that you're taking it, just in case someone else comes along and you duplicate work. Once you have your issue, here are the steps to contribute:
+
 - Fork [xterm.js](https://github.com/sourcelair/xterm.js/)
   ([how to fork a repo](https://help.github.com/articles/fork-a-repo))
 - Get the [xterm.js demo](https://github.com/xtermjs/xterm.js/wiki/Contributing#running-the-demo) running
diff --git a/src/addons/attach/attach.test.ts b/src/addons/attach/attach.test.ts
index 018cfb31..e280b656 100644
--- a/src/addons/attach/attach.test.ts
+++ b/src/addons/attach/attach.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as attach from './attach';
 
diff --git a/src/addons/fit/fit.test.ts b/src/addons/fit/fit.test.ts
index 9a6d89fd..781b5010 100644
--- a/src/addons/fit/fit.test.ts
+++ b/src/addons/fit/fit.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as fit from './fit';
 
diff --git a/src/addons/fullscreen/fullscreen.test.ts b/src/addons/fullscreen/fullscreen.test.ts
index bb98bd30..6d41bdfd 100644
--- a/src/addons/fullscreen/fullscreen.test.ts
+++ b/src/addons/fullscreen/fullscreen.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as fullscreen from './fullscreen';
 
diff --git a/src/addons/fullscreen/fullscreen.ts b/src/addons/fullscreen/fullscreen.ts
index 297a7f5b..4d05e904 100644
--- a/src/addons/fullscreen/fullscreen.ts
+++ b/src/addons/fullscreen/fullscreen.ts
@@ -11,17 +11,18 @@ import { Terminal } from 'xterm';
  * @param fullscreen Toggle fullscreen on (true) or off (false)
  */
 export function toggleFullScreen(term: Terminal, fullscreen: boolean): void {
-  let fn: string;
+  let fn: (...tokens: string[]) => void;
 
   if (typeof fullscreen === 'undefined') {
-    fn = (term.element.classList.contains('fullscreen')) ? 'remove' : 'add';
+    fn = (term.element.classList.contains('fullscreen')) ?
+      term.element.classList.remove : term.element.classList.add;
   } else if (!fullscreen) {
-    fn = 'remove';
+    fn = term.element.classList.remove;
   } else {
-    fn = 'add';
+    fn = term.element.classList.add;
   }
 
-  term.element.classList[fn]('fullscreen');
+  fn('fullscreen');
 }
 
 export function apply(terminalConstructor: typeof Terminal): void {
diff --git a/src/addons/search/search.test.ts b/src/addons/search/search.test.ts
index 243e555c..3e0b8154 100644
--- a/src/addons/search/search.test.ts
+++ b/src/addons/search/search.test.ts
@@ -2,6 +2,7 @@
  * Copyright (c) 2018 The xterm.js authors. All rights reserved.
  * @license MIT
  */
+declare var require: any;
 
 import { assert, expect } from 'chai';
 import * as search from './search';
diff --git a/src/addons/search/tsconfig.json b/src/addons/search/tsconfig.json
index 9998dc1b..c34a0bc5 100644
--- a/src/addons/search/tsconfig.json
+++ b/src/addons/search/tsconfig.json
@@ -18,8 +18,5 @@
   },
   "include": [
     "**/*.ts"
-  ],
-  "exclude": [
-    "**/*.test.ts"
   ]
 }
diff --git a/src/addons/terminado/terminado.test.ts b/src/addons/terminado/terminado.test.ts
index 2e4a53c5..e46eafdf 100644
--- a/src/addons/terminado/terminado.test.ts
+++ b/src/addons/terminado/terminado.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as terminado from './terminado';
 
diff --git a/src/addons/webLinks/webLinks.test.ts b/src/addons/webLinks/webLinks.test.ts
index ce9b8b44..8ada2510 100644
--- a/src/addons/webLinks/webLinks.test.ts
+++ b/src/addons/webLinks/webLinks.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as webLinks from './webLinks';
 
diff --git a/src/addons/winptyCompat/winptyCompat.test.ts b/src/addons/winptyCompat/winptyCompat.test.ts
index 0c9269ed..c3a7e479 100644
--- a/src/addons/winptyCompat/winptyCompat.test.ts
+++ b/src/addons/winptyCompat/winptyCompat.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as winptyCompat from './winptyCompat';
 
diff --git a/src/addons/zmodem/zmodem.test.ts b/src/addons/zmodem/zmodem.test.ts
index 682e62c8..d0c7c5fb 100644
--- a/src/addons/zmodem/zmodem.test.ts
+++ b/src/addons/zmodem/zmodem.test.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-import { assert, expect } from 'chai';
+import { assert } from 'chai';
 
 import * as zmodem from './zmodem';
 
diff --git a/src/addons/zmodem/zmodem.ts b/src/addons/zmodem/zmodem.ts
index 23204f0f..70fc6e98 100644
--- a/src/addons/zmodem/zmodem.ts
+++ b/src/addons/zmodem/zmodem.ts
@@ -34,7 +34,7 @@ import { Terminal } from 'xterm';
  *  via `detach()` and a re-`attach()`.)
  */
 
-let zmodem;
+let zmodem: any;
 
 export interface IZmodemOptions {
   noTerminalWriteOutsideSession?: boolean;
@@ -44,7 +44,7 @@ function zmodemAttach(ws: WebSocket, opts: IZmodemOptions = {}): void {
   const term = this;
   const senderFunc = (octets: ArrayLike<number>) => ws.send(new Uint8Array(octets));
 
-  let zsentry;
+  let zsentry: any;
 
   function shouldWrite(): boolean {
     return !!zsentry.get_confirmed_session() || !opts.noTerminalWriteOutsideSession;