Historically Firefox did have a GDI fallback for certain fonts specifically to address this user complaint, in order to make them look "right". I don't know when/if it was removed.

The pref name is 'gfx.font_rendering.cleartype_params.force_gdi_classic_for_families'. I believe it may have just enabled a GDI compatibility mode for DirectWrite, but I'm not sure if that uses the GDI rasterizer under the hood or not.

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.