After installing Google Toolbar, has Firefox become too slow when opening a new tab? Yes, definetely in mine, Google’s New Tab Page (the page that you see when you open a new tab in Chrome which contains thumbnails of your favourite sites) has decereased Firefox’s performance in a considerable rate.
My solution is to disable this feature until the release of Firefox 3.5 which I believe to be more effective in memory management. Just click on the wrench icon on the toolbar. Under Web-browsing tools uncheck the option Enable New Tab Page.