Proton VPN does encryption and decryption of your account details in the web browser when you log in to your Proton VPN account.
In order to do encryption and decryption in your web browser, we need to use JavaScript for the encryption/decryption and SessionStorage for saving your private key(s) locally. Proton VPN also requires cookies to be enabled so that we can store your current session information and log you into your account.
Javascript
To enable Javascript in your browser, please follow the instructions here.
Cookies
To enable cookies in your browser, please follow the instructions here.