The statement is clear and simple and would not benefit from a TOS rewrite. What you really want are clearer processing directions built into the Firefox UI, not a longer or different TOS.

Something like, a popup over the execute button on the search bar disclosing the specific processing instruction you are providing by pressing that button, and by whom.

Or, when you use a vertical scroll bar, a confirmation that no processing is occurring outside your local machine.

These things would satisfy some more detail-minded people, but ultimately would provide no significant value to either Mozilla or the marginal user, so it's really no mystery why Firefox does not do this.

I guess. But what they really need is trust, which was their selling point for a decade. But that takes a long time to build up and no UX changes can bring back.