Well, maybe it’s not the best title since I’m going to write not only about extensions I’ve been using for long long time, but new (for me) as well.
Grab and Drag is one of the latter, I’ve been using it for only several hours and I simply loved it. It does basically what it’s name says – enables you to scroll web pages how you would scroll PDF documents in Acrobat Reader. It doesn’t block links, you can set hot key for temporary disabling this feature, you can make it switch between ‘hand drag’ and ‘normal’ mode after double click and several more things. Actually it does all I would expect it to do, and more.
One of extensions I TRULY can’t imagine surfing without is Tab Mix Plus. It’s one of most powerful customizable extensions, and one of the most useful. Let me say that it’s option window alone, has 6 tabs (many of which have subtabs). It fixes many of shortcomings of standard Firefox. For example? dbclick open tab to clone it (with it’s history), center clink empty space on tab bar, to bring back last closed tab, see loading progress on every tab, better session management, and many many more. You can have in ff2 ‘close active tab’ button on the left side of tab bar (like in ff1.5).