What Piwik version? What third party plugins? Any local customizations?

It happens on the piwik demo.

http://piwik.org/demo/index.php?module=CoreHome&action=index&idSite=1&period=day&date=yesterday#module=VisitsSummary&action=index&idSite=1&period=day&date=yesterday

Odd. It works for me using FF3.0.x on the demo site.

Can you try deleting your browser cache? (Flash player reportedly also has a cache.) There was a bug in an older version of Open Flash Chart (V2J) that was fixed in V2K.

No feedback received.

It works for me too in FF 3.0, only in 3.5 does it fail.

I have tracked this down to a strange interaction with some firefox extensions and 3.5. On sites which use an embeded "embed" tag under the object tag which loads the flash, this bug is not reproducible. Only on sites which use pure "object" tags to load flash.

Although technically not a piwik bug, I imagine that a large number of piwik users use Firefox, and will upgrade to 3.5 at some point. I guess this could remain closed and the solution is, don't use Firefox with add-ons installed. If more users start noticing this, adding an "embed" tag might patch the upstream bug.

The HTMLObjectElement returned by findSWFGraph() is the expected return type. 'reload' is a function exported by open-flash-chart.swf.

We probably won't add an "embed" hack. We use swfobject which generates standards compliant tags for browsers that support it. We'll revisit this when we update jquery -- it's one of the UI regression tests.