Create row with 'Tab' key sets cursor inside the first Cell of the row

(Only Firefox) Pressing tab in the last cell of last row, creates a new row but the cursor was set outside the table. We manually put the cursor in the first cell of the new row just by calling  firstCell.focus(). This is only a Firefox issue
Merge pull request #1067 from najor/hotfix-rt57686-ff-new-row

Create row with 'Tab' key sets cursor inside the first Cell of the row