Problem with add on- Read Aloud: Text to voice

Hi Firefox, I recently added on your Read Aloud: A Text to Speech Voice Reader Read Aloud: A Text to Speech Voice Reader by Hai Phan ( https://addons.mozilla.org/en-US/firefox/addon/read-aloud/?src=search ) and customized a short cut using shift s to activate the reader. The problem is that shift s doesn't work now for any other function. I no longer have an upper case s by using shift s. I have to use caps lock to get an upper case s. I've contacted Hai Phan's support page and have heard nothing from them. Please help me! I want my BIG s back. Thanks in advance, Clayton