If the quote already has line items, click on the relevant "Line Items Group" to go into that line items group
At the bottom there are some input fields.
In the left input field, start typing a product code (autocomplete from the left by default or double click for fuzzy autocomplete)
Use the cursor keys to navigate the auto complete popup and then press the enter key to select
Selection of a product populates the description and unit price with discount applied.
Tab to the unit price field and change if necessary.
Tab to the quantity field, type the amount and then press the Enter key on the keyboard to add the line item
