Does this plugin work together with the Fooman Speedster module?
If you use Canonical URLs for Magento together with the Fooman Speedster module, you need to overwrite the Canonical module with this download.
I get an error when downloading: “Failed to download …. with preferred state “stable”", how can I fix this?
The reason is you have preferred stability of “stable” and not “beta”. Go the the another tab at your Magento downloader and set it preferred stability to “beta” or “alpha”. It should work now. See the screenshot below for what it should look like: