There seems to be a bug in the latest version of Firefox, where if you right-click on an item and bring up Properties, then you are not able to edit any of the properties.
If you click on an item, and click on Properties in the top menu bar, then you are able to edit Properties.
This is not something our developers are able to fix, as it seems to be an issue in Flash.
1. Open Properties from top meny bar (don't use right-click)
2. OR choose to work in a different browser
Hope that helps!