Third time’s a charm, with tab previews now expected to be included in Firefox 3.6, after the feature was dropped from Firefox 3 and Firefox 3.5
Tab preview provides a visual preview when switching between tabs in Firefox (Ctrl + Tab), much like Alt + Tab when switching between programs in Windows Vista and above.
Tab preview is available in the latest Firefox 3.6 nightly releases but is turned off by default. To enable tab preview, set browser.ctrlTab.previews to true via about:config.
Firefox 3.6 is expected to be released sometime in 2010.