Add Firefox extension link

Author: SaraVieira

packages/chrome-extension/Readme.md

@@ -1,19 +1,28 @@
-# Chrome Extension
+# Browser Extension
 
 ![Image](https://user-images.githubusercontent.com/1051509/46907462-fc0ef600-cf12-11e8-8d73-05b95577364e.png)
 
 [![available in the chrome store](https://developer.chrome.com/webstore/images/ChromeWebStore_Badge_v2_206x58.png)](https://chrome.google.com/webstore/detail/jkhbnhagngalpojoeijaleemepfpefmp)
+[Download for firefox](https://addons.mozilla.org/en-US/firefox/addon/open-in-codesandbox/)
 
-This chrome extension adds a button to all github repos that will open that repo in CodeSandbox in a new window
+This extension adds a button to all github repos that will open that repo in CodeSandbox in a new window
 
-## How to run
+## How to run in Chrome
 
 - Open the Extension Management page by navigating to chrome://extensions.
 - Enable Developer Mode by clicking the toggle switch next to Developer mode.
 - Click the LOAD UNPACKED button and select this folder.
 
 ![load](https://developer.chrome.com/static/images/get_started/load_extension.png)
 
+
+## How to run in Firefox
+
+- Open about:debugging
+- Click "Load Temporary Add-on"
+- Open the extension's directory and select any file inside the extension.
+
+
 ## How to publish
 
-Unfortunately there is a need for a key to in order to update apps so as soon as something gets merged pls ping me in the PR and I will create a new version
+Unfortunately there is a need for a key to in order to update apps so as soon as something gets merged pls ping me at @SaraVieira in the PR and I will create a new version