Comment 33 for bug 548866

This problem is still in precise as of today. A workaround is to uninstall xul-ext-ubufox. For some reason there is a file included (/usr/share/xul-ext/ubufox/defaults/preferences/ubuntu-mods.js) which sets this preference to false. There is a comment included which indicates this is normally true and could be set to false. Fixing the package to have true in that file would seem to be the appropriate fix.

Seamonkey is not affected by this bug and pasting always works.