You can also click on the [+] button that appears before the Main font and Comparison font labels to load fonts into Hibizcus. When the font is loaded, this button changes to [-]. You can click on this to remove the font from the project. When the font is removed the button changes back to [+]. The globe button helps you load system fonts for supported scripts.
In StringViewer, you can disable the display of the comparison font using the options at the bottom of the side bar. In this case, you need not remove the font from the project.
Hibizcus watches for changes to the font files that you load. When you update and export your font from your design tool, the file is updated and you will see a refresh icon next to the font file name in Hibizcus. Just click on this button to update the font to the latest version. If you have StringViewer and/or TraceViewer open, this button will appear there too. You need to click this button on those as well.