The legislation would let Mueller, or any other special counsel, receive an "expedited judicial review" within 10 days of being fired to determine if it was for a "good cause." If it was determined it wasn't, he would be reinstated. It would also codify regulations that only a senior Justice Department official can fire a special counsel and that they must provide the reason in writing.
Prior to this, there was no oversight on Mueller, now there is. Thanks McGruff.