Comment 11 for bug 466567

Saving the required icons from the Humanity icon theme as PNG files definitely works around the issue. With the default "Human" theme an Karmic (which includes the Humanity icons), I can see the right icon for application/pdf in the large attachment view in Thunderbird 3 if I save /usr/share/icons/Humanity/mimes/32/x-office-document.svg as ~/.icons/Humanity/mimes/32/x-office-document.png and make a symlink ~/.icons/Humanity/mimes/32/application-pdf.png to this file.

As far as it is unlikely that moz-icon:// would accept SVG soon enough, it could be preferable to be nice to Firefox and Thunderbird and give them what they want. Setting "package" to "humanity-icon-theme".