> which was/is interpreted by some to be an endorsement of deplatforming.

How else could one interpret it? I'm genuinely curious, as I thought they were pretty clear about it (emphasis mine):

> We need solutions that don't start after untold damage has been done.

> Changing these dangerous dynamics requires more than just the temporary silencing or permanent removal of bad actors from social media platforms.

> Additional precise and specific actions must also be taken:

Imagine that you wanted to advocate against deplatforming, specifically by suggesting better ways to accomplish common laudable goals. However, you can’t argue directly against deplatforming, as this instantly labels you a Trump supporter (and might get you deplatformed). So what could you do?

I am not claiming any secret knowledge about what Mozilla was or is thinking, but what they wrote can certainly also be interpreted in this light, as well.