Active stresses in biological cells and tissues drive many developmental processes. However, increasing experimental evidence suggests that additional mechanical interactions with the surrounding material can play a crucial role in guiding these processes. We introduce a minimal model of this scenario in which the dynamics of a self-organized active fluid subject to inhomogeneous friction can be systematically studied. We show that active stress patterns in such a fluid are pinned by regions of high friction and systematically characterize the resulting mechanochemical pattern-forming instabilities. We find that hydrodynamic screening plays a crucial role in mediating the cross-talk between friction patterns and active fluid self-organization. We further demonstrate that friction patterns can select the length scales of unstable active fluid patterns and identify a mechanochemical frustration mechanism that gives rise to pattern oscillations induced by inhomogeneous friction.