I tire of hearing this repetitively, every time somebody attempts to take this path, but I recognize you are doing it for anybody that is new and didn't hear the other warnings.
Isn't the perfect the enemy of the good?
Can we recognize that this is a good first step, and definitely constitutes a huge improvement over gmail/yahoo type webmail solutions?
You can still quickly add a disclaimer that you hope they quickly begin the large task of development of native windows/mac/linux/ios/android apps that will remove the javascript concern.
If you spit on everything that is not perfect, you may be steering people away from taking any action to protect their privacy.