Microsoft's Tony Schreiner is in charge of the IE7's tabbed browsing features. He posted today about the complications of adding tabs to IE. I still maintain that MS should have hired me to help in this process (quals: 7+ years of IE tabbed browser development) but they weren't interested. Anyway...

Perhaps the trickiest decision MS was whether to break compatibility with 3rd-party IE toolbars. Currently, IE toolbars are "tied" one toolbar to one IE window. But when done right, tabbed browsers save memory compared to single-window browsers because tabs share toolbars. Use the RoboForm toolbar for example. In NetCaptor, you can have 20 tabs open and one RoboForm toolbar - but 20 IE windows would require 20 RoboForm toolbars.

After MS announced IE7 would have tabs, I expected to hear about changes to the add-on APIs to allow IE7 tabs so share toolbar instances. I never considered the possibility that each IE7 tab would have its own copy of 3rd party toolbars. But that's the direction Microsoft has taken. What's the problem with that approach? Every time you open a new browser tab (which tabbed browser users do much more frequently than single-window browser users), you have to create new instances of any 3rd-party bars. Ouch. Opening a folder of 25 Favorites in tabs? You get 25 RoboForm toolbars, and use much more memory and resources than necessary.

Beyond wasting memory and resources, it sounds like IE7 tabs will also waste user interface space. Tony wrote that 3rd party toolbars will now be a part of the tab instead of the IE frame. If I'm reading him right, IE7 could waste valuable vertical UI space, as shown in this doctored screenshot: