A beta version of a web wallet for Masari (a Monero fork) have been released (https://medium.com/@c5d1c1a0c9a8/5e7de6f4919a). It is presented as "Cryptonight’s first client side web wallet". How are its mechanisms different from Mymonero web wallet? What is done server-side on Mymonero but not on this new site?
Disclaimer: I am the creator of this new wallet
When you use MyMonero, your private view is sent to the server (with your public address), but not the private spend keys. It means the server is able so see your balance(EDIT: the server is able to see the incomming amounts, not the outgoing amounts. It means the balance will be off), and the server is precomputing everything for your browser and your browser is doing the final work : checking that the tx are really yours basically.
In the wallet i'm working on with the Masari team nothing is sent to the server. The server is only here to send you the blockchain and that is it. All the decryption is done on your browser. Yes it's using more resources of your computer, but we will never be able to even check your balance. I'm working on improving the performance, but they are currently more than reasonable. In theory, the website could even connect directly to a RPC daemon (not done due to performance issues, but we could and our first prototype did that).
If you need more clarification, i will follow this post and i'm also available on the main masari discord or reddit/r/masari
The Masari web wallet essentially functions as a remote node in the browser directly and sends you all the blocks. The MyMonero web wallet takes your view key and sends you only the relevant blocks.
Masari web wallet offers superior privacy protection. MyMonero offers superior performance.
The Masari web wallet knows when you are connected to the server, when you send funds, and your connected IP. MyMonero knows when you receive funds, when you spend funds or churn, and your connected IP.
The performance gap will grow over time as the Masari blockchain grows.