It's pretty easy to make this mistake if (warning) NS_WARNING("warning"); SomethingImportant(); In debug builds, this does the right thing, but in opt builds, that becomes if (warning) SomethingImportant(); Oops! There's a site in dom/plugins/BrowserStreamChild.cpp where I did this, but it's hopefully being fixed by bsmedberg in some upcoming changes.
Actually, NS_WARNING() et al. prevent this from happening. But I still think it's a useful analysis. Not sure of the best problem definition and approach.