[lxt]

We have several different mechanisms for running experiments. The e10s one specifically runs through what we rather poorly named a "system add-on".

e10s code is present in all builds. The system add-on contains logic that decides whether to turn it on or not. The system add-on can be updated daily (or more often), in all channels.

* I apologize for the naming, this is entirely my fault. I spent a lot of the last twelve months scheming/designing and developing experimental update mechanisms for Firefox.