UPDATE: 10/19/16. It also breaks your attribute editing in some instances:
To fix the product image upload button not loaded in Magento CE 188.8.131.52, I had to add ' character in maxUploadFileSizeInBytes value. Change var maxUploadFileSizeInBytes = < ?php echo $this->getDataMaxSizeInBytes() ?>; To var maxUploadFileSizeInBytes = '< ?php echo $this->getDataMaxSizeInBytes() ?>';
After having applied the latest SUPEE-8788 patch to an Magento EE system, we noticed right away that the “upload” button was missing on the products WYSIWYG view.
Magento Support could find nothing wrong and at the time, no-one had an idea to fix it.
The fix turned out to be extremely easy. Simply, flush every cache/combined JS files, re-index all (from CLI), log out of magento, and clear your browser cache. The upload button came back after doing that. We don’t think the browser cache is necessary, but since it was part of our routine that restored the button, we aren’t messing with the script.