I have been having this issue as well.
Everything seems to load fine using Firefox and Java (which are updated) the only problem is once its loaded (and the picture appears) a warning box appears saying,
before this box appears everything is functioning."Do you want to Continue? The connection to this website is untrusted.
website:
https://secure.cellosoft.com:443Note: This certificate is not valid and cannot be used to verify the identity of this website."
at this point I click "continue". Then it shows me Oekaki, I can move my mouse around and I can hover over the File Edit Layers etc. tabs however the drop-down boxes that appear have no text (its just gray). I also cannot draw or click on anything.
Right now I am running on OS X Lion with 10.9.3 version (maverick) I also have Firefox updated to 31 and Java updated to 7.
--Just tested my JTablet and its functioning normally, and is updated.