I just think perhaps that MsVC++ can only use bmp as icons and can't use other types.
Mozilla displays all the browser with xul (menu, toolbars, ...). This is sometimes an advantage, but this is is also the reason of the low speed of this browser.
We must choose: speed or png... (I'm not against png, I think it's a good format, but necessity is necessity).
A+
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Web:
http://jujuland.pagesperso-orange.fr/
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc