If tools.reader 0.8.4 is included in a project's dependencies, then clojurescript fails to work in a browser, with the error that cljs.core.PersistentArrayMap is undefined. I have created a sample project demonstrating this at https://github.com/jamesnvc/cljs-toolreader-debugging.
I also apologize that I'm not sure if this is a problem in tools.reader or clojurescript. If there is a better place for me to report this issue, please let me know!
OS X 10.9.3, Java 1.8, Clojure 1.6.0