PageDown is not working correctly when editing page with Firefox on Windows

Here is the steps to reproduce the issue:

1. Create a page with a 3x3 table
2. Insert a code macro in the middle of the table
3. Add around 30 line code in the code macro
4. Move the cursor to the top of the page, then press the PageDown button to move the cursor

Expected behavior: the cursor should move to the empty line after the table if pressed the button three times, as 30 lines is around 2 pages string.

Actual behavior: the cursor stuck at the box of first column and second row, no matter how many times we press the button.