According to changes for this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=167601 http://landfill.mozilla.org/mxr-test/mozilla/source/modules/plugin/base/src/nsPluginHostImpl.cpp#3416 ............... * Currently, the default plugin is shown for all EMBED and APPLET * tags and also any OBJECT tag that has a PLUGINURL PARAM tag name. */ ............. OBJECT tag must have PLUGINURL PARAM... According this documentation: http://devedge-temp.mozilla.org/library/manuals/1998/htmlguide/tags14.html PLUGINURL PARAM available only for EMBED tag... see syntax I think this code should be removed - if(nsPluginTagType_Object == tagType && !bHasPluginURL) - return rv; or at least replaced to nsPluginTagType_Embed. In case with default plugin,

that only says that <object> doesn't have a pluginurl attribute. It doesn't say what params it can have...