Ok I did this on my Kindle fire HD which is like a tablet.
So I host my photo on my Facebook. And I look at the photo I want in my album.
Under where you have options to tag the photo you should see Open Photo viewer. Click that.
This brings up a screen with just the photo and comments.
Put your finger on the image and hold down until a menu pops up and choose View Image.
Now put your finger on the url bar at the top. Hold down til you get another menu and choose copy.
Then come to the forum box and put your finger here and choose paste and the copied url shows up like this. https://i.pinimg.com/564x/33/53/b4/3353 ... 7daf88.jpg
Then put the img information that was given in the FireFox instructions and make sure you have the open code and the close code.
