There is an issue with how hterm, Mosh for Chrome's terminal emulator, handles the tab key in Chrome 43, which just got promoted to beta. This will likely affect many users. This was a known issue that was fixed upstream, but I didn't get to it quickly enough. I have just released v0.2.9.17 which incorporates hterm's fix for this problem. Be sure to close all your Mosh for Chrome windows to allow for the update to take effect.