the number of pasting cells is more than the number of copying cells

Steps to Reproduce

1. in a blank sheet, enter 1 at A1, 4 at A4 with *firefox*
2. copy A1:A4 with Ctrl+c
3. press Esc to cancel copy mode
4. move to A5, paste them with Ctrl+v

Current Result

keikai pastes 6 cells instead of 4 cells

Expected Result

pasting 4 cells

Debug Information

• chrome doesn't have this bug
• after Ctrl+v, it produces nested zsfocus

  <div id="_z_25-fo" class="zsfocus" contenteditable="true">
      <div id="_z_25-fo" class="zsfocus">
          <table>
              <tbody>
              <tr>
                  <td>1</td>
              </tr>
              <tr>
                  <td><br></td>
              </tr>
              <tr>
                  <td><br></td>
              </tr>
              <tr>
                  <td>2</td>
              </tr>
              </tbody>
          </table>
      </div>
  </div>
  

Workaround

• https://stackoverflow.com/questions/52817606/contenteditable-in-firefox-creates-2-newlines-instead-of-1
  document.execCommand("defaultParagraphSeparator", false, "br");