How to disable flash in browsers for testing sites?

By the nature of my work, I have to test and check a lot of sites before putting it into practice. Surely, many people know that there is such a problem if flash is installed then flash-will not be displayed, but you can make the system automatically check this, and if there is flash, it shows flash, and if it doesn’t show jpg. the ability to do an intro with flash downloading the correct version).
The question is what, how to disable in different browsers at the time of flash to test sites?
If the opportunity?