RowHeader with incorrect height #361
Description
With recent Firefox versions, I am observing a messed up grid when using RowHeader. Easiest way to reproduce it is to go the Grid Playground, add the RowHeader module and run. Now change the font size with +<+> or +<-> and observe that the height of the RowHeader column will slightly deviate from the height of the data rows. I am often running into this without such manual resizing.
Root of the problem seems to be that the height of the data rows is not an integer, but e.g. 1/6px larger, but the DOM query gives it rounded down.
