In ABP Options > Advanced > Show 'Block element' right-click menu item
Hovering over the (?) sign shows a popup that says "Temporarily block annoying items on a webpage..."
Right-clicking an animated gif, for example, and selecting 'Block element' pops a dialog allowing you to add a filter. This filter is *permanent*, meaning, it will be persisted also in later sessions in that website. From the documentation above, one would expect that block to be temporary.