^ That's probably the right fix, if you want your list items all the
same height. But you will have to insure that you don't put text in the
item that will overflow, otherwise it will now be cut-off.
listview thumbnails aren't meant to fit the height of the item
exactly. The thumbnail is the size of the thumbnail. The height of the
item is dependent on your content (which includes the thumbnail). You
just stumbled on a height that would fit exactly on those items that
have only a heading (not a paragraph) on certain browsers.
On those items with only a heading, the image is taller than the
<a> tag and it's children (heading) and so the height of the
item matches the image exactly because the image is the tallest
element in the list item.
On those items with a heading and paragraph, the padding adds up
to just a bit more, and so you see space below the image because now
the <a> tag is the tallest element in the list item.
This would be more obvious if your paragraph was longer and had
to flow onto a second line.
You get slightly different results on different browsers because
different browsers have different default fonts, with different characteristics.
It's not a jQuery Mobile problem at all - just basic CSS. It's
doing what it is supposed to do. You need to create CSS to give the
appearance you want, rather than relying on an accident of heights
matching-up in one particular circumstance.