The argument is that pressuring Mozilla is a valid second line of attack, on top of pressuring Google. That seems fairly benign, given that Google and Mozilla both have power in the browser ecosystem.

I don't see any assumptions about Mozilla's motive, or think it would be relevant to assume motive one way or another. The assumption is that Mozilla has power to help fuel JPEG XL adoption, so that pressure wouldn't simply be wasted.

Now, I'm not sure it has this power given its 3% browser market share. This might invalidate the particular argument.

That said, there are many valid reasons to give Mozilla execs grief, and many valid reasons to work to deconstruct Mozilla's leadership. So I don't mind if people do it over JPEG-XL, even if Mozilla's had zero power to affect JPEG-XL.