Imgur only allows commenting and voting if you publish it to the community. As long as you don't do that, people won't be able to.
Kindle Fire is a tablet, right? I usually paste things by tapping on the spot where you want it posted, keep your finger on the display until a popup comes that says something like "paste". Tap on paste, and the link will be posted. You will then need to tell the forum that what you posted is a picture, either by highlighting the link text (just as if you wanted to copy it), and then tapping on the icon here on the forum that says "insert image", or by manually entering the code for a picture. To do it manually, you need the opening code right at the front of the picture link, and the closing link right at the end of it - make sure there is no empty space! The opening code is [ img ] and the closing code is [ /img ] (so with a / in it) but without the spaces between the brackets and the text - I had to insert them here in order to make it visible.