diff --git a/README.md b/README.md
index cd181a0..0059fbe 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
     <img src="https://mod-header.appspot.com/images/chrome_1x.png" srcset="https://mod-header.appspot.com/images/chrome_2x.png 2x">
   </a>
   <a href="https://addons.mozilla.org/firefox/addon/modheader-firefox/">
-    <img src="https://mod-header.appspot.com/images/firefox_1x.png" srcset="https://mod-header.appspot.com/images/firefox_2x.png 2x 2x">
+    <img src="https://mod-header.appspot.com/images/firefox_1x.png" srcset="https://mod-header.appspot.com/images/firefox_2x.png 2x">
   </a>
 </p>
 
@@ -23,7 +23,9 @@
 If you find ModHeader useful, please consider making a donation. If you use it for your company project, please ask your company to make a monthly donation!
 
 [![paypal](https://www.paypalobjects.com/en_US/i/btn/btn_donate_SM.gif)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=3XFKZ8PCRB8P6&currency_code=USD&amount=5&source=url)
-<a href="https://www.buymeacoffee.com/scCieVdfj" target="_blank"><img src="https://bmc-cdn.nyc3.digitaloceanspaces.com/BMC-button-images/custom_images/orange_img.png" alt="Buy Me A Coffee"></a>
+<a href="https://www.buymeacoffee.com/scCieVdfj">
+  <img src="https://www.buymeacoffee.com/assets/img/custom_images/yellow_img.png" alt="Buy Me A Coffee">
+</a>
 
 ## Features
 
@@ -41,9 +43,17 @@ If you find ModHeader useful, please consider making a donation. If you use it f
 ## Screenshots
 
 <img src="https://mod-header.appspot.com/images/ss1.png">
-<img src="https://mod-header.appspot.com/images/ss2.png">
-<img src="https://mod-header.appspot.com/images/ss3.png">
+
+## Forking and contribution
+
+Feel free to send pull requests to add new features to ModHeader. It will benefit everyone! That said, I reserve the rights to reject pull requests that does not seem useful, or if they add too much complexity for very little benefits.
+
+You may fork and redistribute ModHeader for a small group of friends / colleagues, but please do not impersonate ModHeader, or try to sell it for a profit. If  you use ModHeader in any commercial product, please let me know.
 
 ## Installation
 
 ModHeader does not require any extra tool for building. Simply load the src directory into Chrome / Firefox to start local development.
+
+## Selenium usage
+
+If you need to use ModHeader for Selenium tests, please visit: https://github.com/hao1300/modheader_selenium