Unfortunately at the time of writing, the beta version 4.0.249, after you close your browser, reopening the tab  fixed there is no trace.

To overcome this problem, make a small change to the link that launches the browser. For example, the Google Chrome on the desktop, just right-click with your mouse, then click Properties. Now in text form called target (ie, the first from top) should look like this:
C: \Users\user\AppData\Local\Google\Chrome\Application\chrome.exe

You just need to add the parameter --pinned-tab-count=x where x is the number of tabs that you want to be fixed at each new opening of browser, followed by the url separated by a single space.

For example if you want to open gmail and reader Add at the end of chrome.exe
--Pinned-tab-count=2 https://mail.google.com/mail http://www.google.com/reader/view/

Launch your browser made in Google, and you have the tabs iconificate permeate.