I've recently published a very simple but useful (at least it adds much comfort for me) FireFox extension.
The idea is simple and can be found integrated into some sites (vk.com, habrahabr.ru) and Opera Mini. Whenever you're reading a page deep down you'd probably want to quickly get to the page top (e.g. while reading Facebook News Feed). Most likely you'll have to use scroll wheel or aim a scroll bar. The easier option is to use a pop-up button (which pops at the right moment) to quickly scroll the page up. That's what the plug-in does.
