Trying to install the Proxtube extension for Google Chrome I cannot drag the .crx file into Chrome. What's wrong?

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http://askubuntu.com – I followed the description on the website but when I try to drag the proxtube.crx file into the Tools tab my Unity launcher to the left gets highlighted and I can't seem to drop the file into Chrome in order to install it. How can I fix this? I'm using Ubuntu 12.04 LTS x64 and Chrome Version 24.0.1312.52 (HowTos)