Thanks, that was great info!When I went into "about:studies", I found "Default UI Experiment - Logo in corner Rollout" and clicked Remove.Then I quit and re-launced Firefox, and everything was back to using the old-style bigger shortcut icons, just ...
It seems like the flag gets flipped back to true on every relaunch of Firefox, probably as part of the "progressive rollout" logic, which undermines this attempted workaround method.
How do you make the change "stick", because even after editing the settings (which fixed it for a little while) eventually the icons went back again to being too small ... and the flag was back to true again!