Please take a few minutes to look through the links I put into the “tips” section of the All In One Favicon settings page.
How to upload a favicon:
1) If you use a WordPress Multisite installation, make sure you add the file type “ico” to the allowed file types property on the
Super Admin -> Options page:
Super Admin -> Options page
2) Go to the All In One Favicon settings page and click on the “Upload Favicon” button next to the favicon you’d like to upload:
Click upload button
3) No, you see the WordPress upload dialog. Click “select files”
Click select files
4) Select the favicon from your harddrive. Now, WordPress will process the favicon and show this dialog:
Upload finished
4) Unfortunately, WordPress 3 omits the “Insert into Post” button at this point, so you’ll either have to select and copy the “Link URL” yourself, click “Save all changes” and paste it into the favicon form field.
Or, you could click on the media library tab, select your newly uploaded favicon and click on “Insert into post” here which will copy the “Link URL” into the favicon form field for you:
Select "Insert into post"