I upgraded to Firefox 4 as soon as it was publicly released with the hopes that I would experience incredible advancements in performance, memory management and new features. Maybe it was the numerous benchmark reviews or release notes but I honestly felt I could feel a quicker firefox, at least for a day or so.  I had a busy work week and after racking up 10+ tabs of opened but unread blog articles, I decided to try out the new Tab Groups option.  What blew my mind was that I couldn't find this feature, I had to google it.   (Customize your toolbar and drag the brick wall looking icon to the Toolbar) After using this feature for a few days, I have started organizing my tabs by category and type.  I have found this feature only slightly more useful then opening a new window and grouping tabs this way.  The thing that blew my mind was that after taking a looking at Firefox's memory usage, I came to the conclusion that Firefox was keeping every page loaded regardless if it was an active tab or a hidden tab group.  I thought for sure, Tab Groups would cache their sites state and then remove from memory but this is not the case.  So I decided to see if anyone else was having the same problem / results / question. I came across a plugin called BarTab which states that on a browser restart will only load the active tab.  The other tabs will be there but not loaded until focused.  Wish I had found this plugin ages ago.  Unfortunately, this plugin doesn't work with the latest Firefox 4.0.1+.  I even tried modifying the plugin install file to force it to work but no luck.  Then I came across a quick little tutorial on CNET that talks about the key BarTab feature that is already part of Firefox.   Just go to about:config in your Firefox address bar, and look for browser.sessionstore.max_concurrent_tabs and change the number to a Zero and restart Firefox.  If you have a large number of tabs, you will notice the browser open very quickly and be very responsive.  The downside is, any unfocused tab will not have their favicon loaded and as you start to load up the different tabs, you will slowly grow the about of memory used. A quick browser restart resolves and resets the memory. Another new feature is App Tab.  I am a big fan of this feature. -If you are like me and need to have a few tabs always open and always visible - like multiple gmail tabs, timesheet or workspace tabs, etc. this is the feature for you.  Just right click on a tab and select Pin as App Tab. This will shrink the tab to just its favicon and pin it to the left. Now, this tab will always be visible even if you have enough tabs open to cause tab scrolling.  The best part is that gmail will still highlight when you get a new email. Hope this was helpful.