For images, you can turn off automatic downloading here:

orange Firefox button or classic Tools menu > Options > Content

Then, to fetch them for a particular page, you can try an add-on such as Show Picture.

For content that plays in plugins, I'm not sure whether there is a universal solution. Perhaps there is an add-on that does it globally, otherwise you might need to pick up individual ones such as Flashblock. (Note: I haven't tried it myself.)

Edit: Also not sure about HTML5 audio/video. There might be a way to stop it from auto-playing.

thanks - back in the days when i used IE there was a place in its options where all this disabling could be done in one place, and then, if one did want to see an image or view a video or hear something all one had to do was R-click and get whatever was needed back immediately (for that one occasion only). I was hoping for the same thing-- a simple solution to simplify my life and not have to go crazy configuring bla, bla bla. Once again buddy, thanks