mCompatibilityMode = aMode;  if (!mShell) return;
if (! mCompatibilityLocked) { mCompatibilityMode = aMode; }
nsPresContext::SetCompatibilityMode(nsCompatibility aMode){  mCompatibilityMode = aMode;  if (!mShell)    return;  // enable/disable the QuirkSheet  mShell->StyleSet()->    EnableQuirkStyleSheet(mCompatibilityMode == eCompatibility_NavQuirks);}