It's quite a practical extension to have, as the things it blocks are usually banners or large items that slow down your connection speed, making Firefox run slow.
Flashblock works with Macromedia Flash, Macromedia Shockwave, and Macromedia Authorware content. To use it, just install and activate the extension. Then, whenever you visit a page with Flash, that element will no longer load automatically. In its place you see a button – if you want to see the item that was blocked by Flashblock, just click it.
Firefox 1.5 to 3xNetscape 9.