From ydn-javascript:

If you're having problems because there are other libraries which depends on an other Mozilla Rhino implementation you can do the following so that the YUICompressor uses
its own Rhino version exclusive (to the YUI developer: Please do this with your binary release):

1. Download JARJAR from http://code.google.com/p/jarjar
2. Create a rules file (e.g. yui-rules.txt) with this content:

rule jargs.gnu.** com.yahoo.platform.yui.@0
rule org.mozilla.** com.yahoo.platform.yui.@0
keep com.yahoo.**

3. Generate a new YUICompressor JAR with all(!) classes inside the com.yahoo.platform.yui context so no more library conflicts will be possible:

java -jar jarjar-1.0.jar process yui-rules.txt yuicompressor-2.4.2.jar yuicompressor-jarjar-2.4.2.jar

Now use the newly created yuicompressor-jarjar-2.4.2.jar in your app.