We recently upgraded an iMac to Yosemite. Ever since the upgrade, Safari and Chrome cannot play Quicktime videos. It claims "Plugin Failed". Chrome wants us to activate the plugin, as if it were not installed. Chrome confirmed the extension was there and was enabled.
It leads us to a link on Apple's website which tells us that Apple updates Quicktime plugins automatically through "Software Update". It appears our version of Quicktime (Quicktime X) was up-to-date. However, the "Open With" options for Quicktime videos included Quicktime X, and Quicktime 7.6.6 Removing Quicktime 7.6.6 didn't help. Trying to install 7.7 wasn't allowed since Quicktime X was already there.
However: when we downloaded and installed Firefox (which hadn't been on the system), Firefox played Quicktime videos. Uninstalling and Reinstalling Chrome didn't help.
Anyone have thoughts on this?