Problem with Firefox and Description Field

-- HikaShop version -- : 6.5.0
-- Joomla version -- : 5.4.0

Hello,

I have a problem with Firefox and Description Field.

I cant edit that field (write or add more info for the product) and at the back end it isnt steady, it flickers. At the front end there is not such problem, the existing information displayed to the user.

I am using TinyMCE.

At Chrome the problem disappears and it is working normaly.

Any ideas how to fix it?

Thank you in advance.