I want to write a letter to say goodbye to a developer because today I have deleted his extension. My native language is not english, thus can you help me to write it. include those below to your letter and extend.

I been using your extension about 4 years right now. I am pretty sure that this idea came before many of people before and still I am very curious about how you had managed to keep this app so relevant on those 4 years.

This was one of the softwares that I am so greatful that you have implemented.
user