I see the discussed web page is quite heavy in terms of widget count. The TabStrip is the last widget to be initialized, so the observed issue is not unusual.
You have several options:
1. Rework the page, so that some widgets are initialized client-side on demand instead of initially.
2. Use tabs loaded with Ajax
3. Apply a visibility:hidden style to the TabStrip or its parent element, and remove it after the widget has been initialized.
Following general optimization guidelines is always welcome. For example, move all CSS from the <body> to the <head>.
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