<tr v-for="(unfilm) in film" v-bind:key="unfilm.key">
 
   <td>
                      <div id="titolo">{{unfilm.titolo}}</div>
    </td>
	
	   <td>
                                <img :src="unfilm.locandina" style="max-width: 50px;">
       </td>
	   
	    <i @click="cancellaFilm(unfilm)" class="material-icons deep-orange-text text-darken-4"
            style="cursor: pointer;">delete</i></td>
			
			
			cancellaFilm(unfilm) {
			  gamesRef.child(unfilm['.key']).remove()
			  
			   this.$toastr.info('Errore', 'Attenzione');
          //  this.$alert("Film cancellato")
        }
  }

回答如下：

在cancellaFilm()功能中，unfilm['.key']是undefined。

执行

gamesRef.child(unfilm['key']).remove()

代替。