This might be late but thanks a lot Caravel for finding the extension. And a quick tip for easier surfing: To be able to view the history manager in new tab or sidebar (looked not properly though) go to View > Toolbars > Customize... and drag the 'Enhanced History Manager' into your Firefox Toolbar. Then, you can choose whichever view you wish.

Just my thought: It'll be better if it is somehow integrated into the history sidebar with IE look (the current EHM Sidebar looks improper) that way it'll be much simpler.

Still, it's much much better than without the extension.