As Giorgio and Ilna said, the bug happens when copying something from netbeans and right clicking on firefox bookmarks toolbar.
I found what is the problem, it seams to happen when using netbeans installed from ubuntu repositories. One of the requirements of this package is OpenJDK and I think it's the root problem.
My work around was to uninstall netbeans and OpenJDK and install the package sun-java6-bin + netbeans downloaded from netbeans.com
As Giorgio and Ilna said, the bug happens when copying something from netbeans and right clicking on firefox bookmarks toolbar.
I found what is the problem, it seams to happen when using netbeans installed from ubuntu repositories. One of the requirements of this package is OpenJDK and I think it's the root problem.
My work around was to uninstall netbeans and OpenJDK and install the package sun-java6-bin + netbeans downloaded from netbeans.com