The latest update of Firefox 3.6, is the one that integrates better with Windows 7. One of its features is that you can turn on the thumbnails of the tabs in Firefox. That is, now when you hover your mouse pointer over one of the icons in the taskbar, Firefox shows the thumbnail of the active tab.
With the next tip you can activate the thumbnails of all your open tabs in Firefox:
Open a new tab and write about: config in adress bar, then press Enter and accept the warning notice.
Then go to the search box and look browser.taskbar.previews.enable, you double-click to change from false to true.
Finally restart the browser, open multiple tabs, you minimize it and pass the mouse over the Firefox icon and you will see the change. (screenshot below)