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What is the Refresh Rate

By default Firefox updates microsummaries every 30"

Is it possible to change the refresh rate

Yes, but by changing Firefox settings (http://kb.mozillazine.org/Browser.microsummary.updateInterval)

In Firefox: 1. open the configuration panel (about:config) 2. add the Integer Preference Name named: browser.microsummary.updateInterval and set the value in minutes.

Are other browsers supported

Not at this time. The Microsummaries are only supported by Firefox 2+ so far. You should ask your browser vendor to implement