I have an HTC One that I recently replaced my Galaxy Note with and I absolutely love the phone. That said, I ran into an interesting problem with an outright mind boggling solution. I recently upgraded the firmware to Android 4.3. Today when I attempted to run an app on it, developer mode isn't enabled. So part of the upgrade apparently turned it off. Then I went into the settings and… no developer option.
To enable the developer menu option, go in to settings and select:
Now click Build number 7 times. After tapping a few times, you will get a notice.
After you do this, the developer menu will now be shown:
Very odd experience.