If the algorithm is correctly implemented, Javascript encryption is no worse than any other.

The problem with JS is that the browser may be not good enough, failing to prevent certain attacks from other tabs.

The OS may be compromised, too, so that the data is available before encryption, or the key phrase gets stolen and siphoned out by a keylogger. However good your software is, you can't fight against it.

As memory is getting cheaper, running each domain in a different process in a different container or VM becomes more feasible (see Qubes OS). In a well-insulated environment, JS encryption should be as safe as any other.

True. But if what you say is true, that the encryption in javascript is good enough or comparable to their desktop counterparts, then it is a step in the right direction.

Nothing is 100% secure, specially in the web, but anything is better that what we have today.

I will start doing some research on the solutions to this. We are going to do for our clients, what I expect my providers do for me.