I think this question arises primarily from my insufficient understanding of browser caching. Let's log in to ProtonMail, and read a message. My understanding is that an encrypted 'blob' of data gets downloaded by my browser, and it gets decrypted locally. Can ProtonMail ensure my browser will not cache the text, readable after the decryption? Can I ensure it with some straightforward local method, preferably without plugins?
I did not specify any web browsers.