I'm trying to install unity-webapps-preview, so I previously added the PPA :

    $ sudo add-apt-repository ppa:webapps/preview

    $ sudo apt-get update

but I get the following error :

    $ sudo apt-get install unity-webapps-preview

    Reading package lists... Done

    Building dependency tree       

    Reading state information... Done

    Some packages could not be installed. This may mean that you have

    requested an impossible situation or if you are using the unstable

    distribution that some required packages have not yet been created

    or been moved out of Incoming.

    The following information may help to resolve the situation:



    The following packages have unmet dependencies.

    unity-webapps-preview : Depends: xul-ext-unity but it is not going to be installed

                            Depends: xul-ext-websites-integration but it is not going to > be installed

                            Depends: xul-ext-webaccounts but it is not going to be installed

    E: Unable to correct problems, you have held broken packages.

I tried to manually install the dependencies and I get :

    $ sudo apt-get install xul-ext-unity xul-ext-websites-integration xul-ext-webaccounts

    Reading package lists... Done

    Building dependency tree       

    Reading state information... Done

    Some packages could not be installed. This may mean that you have

    requested an impossible situation or if you are using the unstable

    distribution that some required packages have not yet been created

    or been moved out of Incoming.

    The following information may help to resolve the situation:



    The following packages have unmet dependencies.

    xul-ext-webaccounts : Breaks: firefox (>= 14.+) but 15.0.1+build1-0ubuntu0.12.04.1 is to be installed

    E: Unable to correct problems, you have held broken packages.

Version of Firefox : 15.0.1

Version of Ubuntu : 12.04