If you push hard, it will slide right off the table. If you push against it very lightly, it won't move. Intuitively, you know a block of wood will slide with a lighter push than a hunk of rubber, and the wood block will also be easier to move than a block of lead. You can see from this equation that the friction force is larger when Cf is larger. Cf is why you have to push a rubber block harder than a wood block.
Rubber sliding on anything has a higher Cf than wood sliding on that same material.
Fv, the vertical force, is why it takes more force to slide a lead block than a wood one. The lead is heavier and so Fv is bigger than with a wood block of the same size. Rubber has a relatively large friction coefficient when tested on most surfaces. Let's say it's 0.8. If the rubber block weighs 1 pound, then the vertical force is 1 pound, and it's going to take 0.8 pounds of force to push the block at a steady speed.