Query only slow on first run

I have a query that takes about 7000 ms in average to complete the first
time it runs. Subsequent runs complete in only 50 ms. That is more than
a factor 100 faster! How can I make the query perform good in the first
run too?

Query and output from both first and second run of Explain Analyze is
pasted here:

http://rafb.net/p/yrKyoA17.html