Occured when the cell contained any block content with a differnt line
height to the table cell itself.
In firefox, cells with a height would end up with an actual greater
real cell height, which messed up TinyMCE resize calculations, causing
tables to grow.
Adding default vertical-align: top, changes this behaviour to get proper
cell heights.
Related to Firefox issue: https://bugzilla.mozilla.org/show_bug.cgi?id=569645
Have tested that editor cell text align options can still be used with
this.
For #4337
5ea2d0c57b