Hi,
With a link to your store it would be easier for me to tell you (and make some tests).
In Firefox, you can open the error console in web development menu or by using the shortcut: Ctrl+Alt+J
The "Error" tab would give you the errors in the page, just clean it before opening the product editing page in order to see if there is a javascript error.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.