End-to-end encryption is useless without endpoint security, i.e. security of the device you're using. As far as I can tell, all new chips have something like the Intel Management Engine, which allows out-of-band access to the device. It takes about 6 lines of VHDL to modify a CPU so that if it receives a specific combination of instructions, it will transition to ring 0. That could even be added to the microcode so you wouldn't even be able to find it with a microscope. That essentially means if someone knew the right combination of instructions, a simple javascript expression could give you kernel level access to the machine.