Kubuntu 12.04 LTS

[rms]

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When I select the "force version" option in Muon, the 12.0 version gets installed anyway.
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In all honesty, I'm myself new to Kubuntu and I haven't used Muon very often(relying on cli). Maybe it's a bug?

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Do I just use the whole name, like sudo apt-get install firefox-11.0+build1-0ubuntu4 ?
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Yes. use the full name of the package.