It most certainly uses GDI for Verdana. Firefox tried to disable that by overwriting the previous default setting for gfx.font_rendering.cleartype_params.force_gdi_classic_for_families and gfx.font_rendering.cleartype_params.force_gdi_classic_max_size, but restoring them fixed that.
Also this is not important. What's important is that DirectWrite does not render this font correctly, if you compare it with LibreOffice or Word.
Also this is not important. What's important is that DirectWrite does not render this font correctly, if you compare it with LibreOffice or Word.