Unlike many people, my usage of Firefox 3 has been restricted to test and virtual machines. Thus, I may have stumbled across a bug that goes unnoticed on more actively used systems. There seems to be a problem installing the Flash and Java plugins, at least on Windows machines.
Firefox 3 obviously works fine with both Flash and Java, assuming they are already installed. But, if you try to view a web page that requires either plugin, clicking the "Install Missing Plugins" button (shown below) doesn't work, at least on four Windows machines that I tested.
On a Vista machine, Firefox never found the missing plugins, either Flash or Java. It just kept searching and searching. On Windows XP, both plugins were "not available" (see below). I tried this on XP Home and Professional and with both a normally installed copy of Firefox 3 and with the portable version. I even tried this on Windows 2000 and got the same results as with XP. None of these Windows machines had any anti-malware software installed.
It's not all bad news. Every time I manually installed the Flash and Java plugins things went fine.
To test this yourself with Java, you can use the version page at my JavaTester.org site. To test Flash, try the Adobe Flash tester page. You can double check that neither plugin is installed by entering "about:plugins" in the address bar, without the quotes.
I haven't tried this with other plugins and not being a Mac person, haven't tried it there either. But, I did try it under Ubuntu 8.04 where the auto-install of both plugins ran fine (but you may have to restart Firefox).
My best guess is that this is a Firefox bug. If you're running Firefox 3, and don't have one of these plugins already installed, please try it and let me know. You can email me at michaelhorowitz at gmail. Thanks.