Bookmarklet for using this sitetest: Test page. (Right-click this link and select add to bookmarks.)
Version that opens new window: Test page
New: bookmarklet for listing external scripts on page: List external scripts (Right-click this link and select add to bookmarks. This works in browsers with good DOM support, O07, Moz etc.)
Note that often there are good reasons why Opera Software has chosen not to implement features. Since this is not a validation service, those reasons will not be discussed here. Please don't send Opera Software bug reports and complaints based on this test, they already know every detail about the lack of support for the functions this page tests for.