PVS-Studio warning V501 for Firefox

static PRBool IsZPositionLEQ(nsDisplayItem* aItem1,
                             nsDisplayItem* aItem2,
                             void* aClosure) {
  if (!aItem1->GetUnderlyingFrame()->Preserves3D() ||
      !aItem1->GetUnderlyingFrame()->Preserves3D()) {
    return IsContentLEQ(aItem1, aItem2, aClosure);
  }
  ...
}

Most likely this is what should be written here: !aItem1->.... || !aItem2->....

This suspicious code was found in Firefox project by PVS-Studio static code analyzer.
Warning message is:
V501 There are identical sub-expressions to the left and to the right of the '||' operator. nsdisplaylist.cpp 767

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/