c.f. https://matrix.to/#/!zvtoFTlOBeOwHrBlEK:matrix.org/$yumW_YPZ6kAsKlD3SB_muMP9ImAUoF893INwdNegTEw?via=matrix.org&via=mozilla.org&via=igalia.com

Nowhere does https://w3c.github.io/webdriver/#dfn-matching-capabilities match setWindowRect, so it effectively is ignored when passed as a capability (see: #1792).

However, per @whimboo:

In Firefox we match that capability and fail if the value is not appropriate

I have not tested what other implementations do.