I installed this as /usr/local/bin/rhythmbox-wrapper and made it executable with chmod +x /usr/local/bin/rhythmbox-wrapper. Then, just click the pls file link on the website. When Firefox asks you what to do with the file, specify "other" and point to /usr/local/bin/rhythmbox-wrapper.
SOLVED
I got this to work. Here's the script:
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#!/bin/sh
rhythmbox $1
cat $1 | grep ^File | head -1 | awk -F= '{print $2}' | xargs -i rhythmbox-client --play-uri={}
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I installed this as /usr/local/ bin/rhythmbox- wrapper and made it executable with chmod +x /usr/local/ bin/rhythmbox- wrapper. Then, just click the pls file link on the website. When Firefox asks you what to do with the file, specify "other" and point to /usr/local/ bin/rhythmbox- wrapper.
Cheers!