I will stick to the "clearly false" since it is now well to the point where we are in 2019-05-04 (even in local UT1, let alone UTC), studies are disabled (and have been since forever), no studies have been loaded, and my extensions still work quite fine, thank-you. Attempting to install a "new" extension fails with a "bad signature" error.
Here's something interesting - a few times now, I've told Firefox to enable Studies and then restarted ... but the Studies setting reverted to being unchecked.
Maybe one of my other paranoia-enabling extensions is toggling it off ... but if so, I haven't found it yet. Still investigating.
Even stranger, I can manually toggle 'app.shield.optoutstudies.enabled' in about:config ... and *that* persists across reboots ... but Studies *still* aren't enabled (the about:preferences item is still unchecked, and the "about:studies" area still indicates that they're disabled).
There's definitely something weird about enabling/disabling studies.
FWIW, this is 64-bit 66.0.3 on Ubuntu, and it's an instance of Firefox that had studies disabled before this issue emerged. On a very similar setup, but one with a vanilla Firefox install that already had Studies enabled, I can't recreate this symptom - even if I turn Studies off (either using the GUI or with the about:config item).