Want to add jquery to a page you are viewing on your browser for some quick hackery?
Create a bookmark with this as the location:
javascript:void((function(){j=document.createElement("SCRIPT");j.src="<a rel="nofollow" target="_blank" href="http://code.jquery.com/jquery-latest.pack.js" class="ot-anchor bidi_isolate" jslog="10929; track:click" dir="ltr">http://code.jquery.com/jquery-latest.pack.js</a>";document.getElementsByTagName("HEAD")[0].appendChild(j);})())
Whenever you use the bookmark it will add jquery to the current page, then just open up your javascript console and hack away.