I just upgraded to WP3.6 and I've noticed some odd behaviour with tables. Clicking between cells seems to be a bit buggy - the selection follows your mouse as if you were dragging. It appears that you need to hover over the cell with your mouse in order to enter content.
This makes adding images into aa table cell difficult. You need to add the image to the page and then (carefully) cut and paste the image into the cell. The text cursor disappears from the cell once your mouse leaves.
I've noted this behaviour on both Firefox and Chrome (latest versions of both). The mystery selection thing happens more often than not (but not always) in Firefox. In general, though cells can be somewhat more difficult to select.
This was flawless before WP3.6
I've uploaded a quick vid here to illustrate in case my description is unclear: