How can I add a font to the Font Book Web Collection
This is not really an answer but these questions may help you narrow down the issue and ultimately resolve the issue.


After the Drag &amp; Drop operation is complete, does the font show in Web collection ?
If it shows, does the font have any Yellow Exclamation mark on it ?
If yes, try repair it
If you do not see the font there, Right Click on Web Collection and Click Add fonts, then locate the font in Fonts folder from System Library or Local Library