FF Fix: missing scrollbars on inner_cells

IPython/html/static/notebook/less/cell.less

@@ -1,47 +1,50
 div.cell {
     border: 1px solid transparent;
     .vbox();
 
     &.selected {
         .corner-all;
         border : thin @border_color solid;
     }
     
     &.edit_mode {
         .corner-all;
         border : thin green solid;
     }
 }
 
 div.cell {
     width: 100%;
     padding: 5px 5px 5px 0px;
     /* This acts as a spacer between cells, that is outside the border */
     margin: 0px;
     outline: none;
 }
 
 div.prompt {
     /* This needs to be wide enough for 3 digit prompt numbers: In[100]: */
     min-width: 11ex;
     /* This padding is tuned to match the padding on the CodeMirror editor. */
     padding: @code_padding;
     margin: 0px;
     font-family: @monoFontFamily;
     text-align: right;
     /* This has to match that of the the CodeMirror class line-height below */	
     line-height: @code_line_height;
 }
 
 div.inner_cell {
     .vbox();
     .box-flex1();
+
+    /* This is required for FF to add scrollbars when code cells overflow. */
+    overflow: auto;
 }
 
 /* This is needed so that empty prompt areas can collapse to zero height when there
    is no content in the output_subarea and the prompt. The main purpose of this is
    to make sure that empty JavaScript output_subareas have no height. */
 div.prompt:empty {
     padding-top: 0;
     padding-bottom: 0;
 }