User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:15.0) Gecko/20100101 Firefox/15.0 Build ID: 20120808131812 Steps to reproduce: Playing with the jQuery+CSS3 example here http://tympanus.net/Tutorials/SwatchBook/index2.html I notice a strange issue on this iMac (CPU: Core i5, GPU: AMD Radeon 6750M 512 MB) which I do not notice on an older iMac (CPU: Core i3, GPU: AMD Radeon HD 4670 256MB). The rest of the relevant software stack was the same for both computers: Firefox 14.0.1, OS X 10.8 Mountain Lion, same set of extensions, etc... Actual results: On the newer iMac (CPU: Core i5, GPU: AMD Radeon 6750M 512 MB) I could notice non trivial screen tearing and I did check and HW acceleration was enabled and active. If I manually disabled it (deactivating the layers acceleration option, by setting the layers acceleration disabled flag to true) I would not notice anymore tearing in the animation. On the older iMac (CPU: Core i3, GPU: AMD Radeon HD 4670 256MB) I had no tearing problems with layers acceleration enabled and the same web page. Also, this seems to have been fixed in Firefox 15.0 Beta (downloaded it today, 08/15/2012) as I see no more tearing artifacts on that web page and with layers acceleration enabled. Expected results: The CSS animation should have occurred without any screen tearing artifacts.
Closing this old bug report. Goffredo, please reopen this bug report if you can still see the issue.