Two questions rolled into one.
Can browsers in general cache a URL (js script) if it's requested with URL variables? E.g. www.thing.com/?l=lib&s=thing.js
Can browsers cache a file if it is a php redirect? E.g. www.thing.com/script.js (called, is a php file with a redirect to www.thing2.com/actual.js)
Thanks.
Since you have two questions
Can browsers in general cache a URL (js script) if it's requested with URL variables? E.g. www.thing.com/?l=lib&s=thing.js
Yes.
Can browsers cache a file if it is a php redirect? E.g. www.thing.com/script.js (called, is a php file with a redirect to www.thing2.com/actual.js)
Depends. If the redirect is a 301, then yes per the spec
If the redirect is a 302, then maybe