Text select disabled when editing invoice descriptions - Mac using MYOB Business through Frirefox

When updating an invoice, I used to be able to hightlight the text in the 'description' field and copy and paste. There was also the ability to edit text in the description field by placing your cursor when you wanted it and changing or adding text. 

From a week ago I can no longer highlight description text in invoices, the cursor only wants to be placed at the end of the description and I need to use my up and down and left and right arrows in this field.  Double clicking to select a word, or all text in this box doesn't work?

This is very frustrating, is anyone else experiencing something similar. 

(The screenshot shows where the cursor appears no matter where you place in the description field, you can't select text in this field any more, just move the cursor with left, right and up and down keys)