Firefox/Gecko iframe doesn't render, is this a browser bug?

We have a public Cognos 8 BI reporting solution running inside an iframe. Cognos 8 BI supports Firefox and IE. IE works fine. With Firefox 3.6.13 (the current version) when the report parameters are changed the iframe is often not rendered but is left completely white. This never happens with IE, Firefox 3.0.18, Firefox 4.0 beta 9 or if the report was开发者_如何转开发 opened directly without an iframe. Are we facing a Firefox iframe rendering bug? Debugging with Firebug indicates that all content gets loaded by Firefox but it just never displays.

This is how to reproduce: start Firefox 3.6.13 on Windows (don't know if it reproduces on Mac or Linux, reports are welcome). Go to https://sampo.thl.fi/select?area=ESHjono and let the report load completely. Yes it is all Finnish :-D On the topmost dropdown box change from Parivertailu (first selection) to Aikasarja (third selection). A vertical bar report should load. Now change any report parameters in the three dropdown boxes on the report (SAIRAANHOITOPIIRI, Erikoisala, Hoitoa odottaneet yli 180 vrk (%)) to any values. Very often the report is not updated but is left completely white. But if you load the report directly without an iframe via https://sampo.thl.fi/launch/ESHjono-report-aikasarja-prod and change the same parameters there, it gets updated every time. Strangely the issue can be reproduced also on Nokia N900 Maemo Browser (unsupported by Cognos 8 BI). So it might be a Gecko iframe rendering bug, not just something to do with Firefox.