Widgets related issues in 1.7.2-rc8:
1) There is no visual feedback on Firefox (11.0) while widgets are loading. I.e., the "Loading Data..." disappears quickly with appearance of the "Widgets & Dashboard" selectors, long before the widgets appear, so that one is left wondering if something is still to arrive or not.
(Whereas on IE8, the "Loading Data..." stays, with the "running bars" to its left hand side "frozen" (which is fine, as one sees that the page has not yet fully loaded) until the widgets appear. I didn't check other browsers.)
2) The "Visitor Countries (World Map)" widget does not get displayed properly in Firefox (11.0) (but it does in IE8). It shows "Displaying Graphs in Piwik requires Flash".
(Just for info: The "Last Visits Graph" widget also behaves differently, showing the zeroed graph where the one on 1.6 showed the "no data" message. But I guess that is expected, as an alignment to the behavior of the "Visitors in Real Time" and "Visits by Server Time" widgets.)
Same behavior with Firefox 12.0.