I suppose you want protection from server compromise if you require client-side encryption. However, you should be mindful that if the code that encrypts your content is served by your server as part of a web interface, then an attacker can simply alter the code that is sent to your browser to leak your master password, or your files. If you want secure client side encryption, you cannot rely on a code that is served by your server either. You will need to install an app.