Comment 12 for bug 418633

I am experiencing this too but I have some further insight into the problem:

As mentioned, gnome-font-viewer fails to install a font if it is already installed. But it ONLY fails if the filename is the same.

In fact, the application fails to install if you try to install ANY font having the same filename as a previously-installed font!

It makes no attempt to determine whether the same font is actually installed. It just blindly copies the file to the ~/.fonts directory when you click "Install".

Steps to reproduce:
1. Clean out your ~/.fonts directory (or not, but might as well)
2. Use gnome-font-viewer to Install a font from a file, perhaps 'webfont.ttf'
3. Try to repeat step 2

Expected behavior:
It should check the (internal) font name, say "Arial". If "Arial" is already installed (from any filename), it should say so. If not, it should allow a user to install the font.

If the font really isn't installed yet, it should automatically rename conflicting files via a standard "append counter" sort of conflict resolution algorithm. That is, if a file called 'webfont.ttf' is already installed (but the enclosed font is not), the newly-installed font should be stored in 'webfont1.ttf', or 'webfont-2.ttf', or something along those lines.