I ran Page Speed on my blog and got the following recommendation:
Remove query strings from static resources
Enabling public caching in the HTTP headers for static resources allows the browser to download resources from a nearby proxy server rather than from a remote origin server.
Here is a sample URL it references:
The part after the question mark is added by W3 Total Cache. Whenever settings are changed, a new query string will be generated and appended to objects allowing the new policy to be applied. In order to prevent this, you have to go to the W3 Total Cache settings, Browser Cache and uncheck Prevent caching of objects after settings change.
With this change, your Page Speed score will increase and you can take care of the next issue 😉