This is either astoundingly bad reading comprehension, or a willful mischaracterization. The whole article is about what they're doing to prevent Spectre-like problems. The config option is their backup plan in case they made a mistake in their threat analysis.
All in all, I thought it was a sober and mature approach to the problem.
`about:config` -> `dom.workers.serialized-sab-access` -> true
Otherwise you risk sites opting in to Spectre. Why Mozilla thinks this is a good thing is beyond me.