We read
$wgMobileFrontendLogo false, default no logo URL to the logo used in the mobile view. Should be 35 × 22 px.
However in the code it says
/** * Path to the logo used in the login/signup form * The standard height is 72px * FIXME: Merge with $wgMFCustomLogos */ $wgMobileFrontendLogo = false;
So it turns out this logo is not 35x22, and it only appears on one form, not every page as one would assume.
