All my Icons display as blank boxes, how do I fix this?

H5 can manage icons in multiple ways
The default is to use PNG instead of Icons, it translates the icon name to .ico.png

Icon batch conversion program Diego posted on the newsgroup 21/10/2016, uploaded to Github for convenience:

If you prefer to use the old icons you have to call the
SoftVelocity recomend the use of PNG icons, then you can modernise the images changing only the web ones.