Using Custom icons (included inside custom icons folder)

1) find out your icon's bundle ID, copy/rename and place it in IconBundles folder of base theme (or your custom theme)
E.g. com.apple.mobilesafari-large

2) rename the same image's GIF file inside Icons folder (e.g. com.apple.mobilesafari) without -large


Thx to yakitori2009 for his great work and help by tito12