This would make it run on firefox 4 and 5

Please note that firefox 4 and 5 changes how xul is handled. Simply changing the supported version will cause some backgrounds to be missing from context menus (right click) and exporting images or using pages as background won't work if the stencil contains any XUL. Also sandbox evaluation has become more strict which breaks some stencil definitions.

See http://pencil-ff4.googlecode.com where some of these issues have been addressed. The whole thing is a work in progress though.

Also please update issue 291, issue 292, issue 298, issue 300, issue 306 etc if progress on this issue occurs.