I recently discovered a nice set of shortcuts that use the middle mouse button click:

• In Firefox or Internet Explorer, middle-clicking on a link will open that link in a new tab.
• In Firefox or Internet Explorer, middle-clicking on a tab will close that tab. This also works to close files in Visual Studio.

I’ve started to use these and find myself using them all the time. Apparently middle-click is useful in Windows 7 as well.

For more juicy Firefox shortcuts:
• Ctrl-T for a new tab
• Ctrl-W to close the currently active tab
• Space and Shift-space to page up/down
• Ctrl-F to find
• Ctrl-Tab/Ctrl-Shift-Tab to go forward/back one tab

And my two best Windows shortcuts, which I can’t live without:
• Ctrl-Shift-Esc – bring up Task Manager
• F2 in Explorer – rename a file

Thanks also to http://www.knowledgesutra.com/index.php/15-firefox-tricks_t49240.html for some nice tips.