I did notice that inside Firfore Options>Network Blockchain.info is listed as 'allowed to store data for offline use'
I've removed that listing, no idea if Blockchain put it there or a hack of some kind.
https://blockchain.info/wallet/securityLocal storage
No sensitive data is stored in your browser's local storage. If available the site will cache your wallet identifier, address balances and transactions, in the event of login with a different identifier this data is cleared