Darken Script No Longer Working?

I use a Greasemonkey script called Darken in Firefox that I got from this page: http://lifehacker.com/259456/invert-web-page-colors-with-the-darken-bookmarklet . It inverts webpages to a black background with bright grey text for easier reading. Now that I've upgraded to Firefox 37.0.1 and Greasemonkey 3.1, it doesn't seem to work anymore. The actual script is

javascriptfunction(){var%20newSS,%20styles='*%20{%20background:%20black%20!%20important;%20color:%20grey%20!important%20}%20:link,%20:link%20*%20{%20color:%20#0000EE%20!important%20}%20:visited,%20:visited%20*%20{%20color:%20#551A8B%20!important%20}';%20if(document.createStyleSheet)%20{%20document.createStyleSheet("javascript:'"+styles+"'");%20}%20else%20{%20newSS=document.createElement('link');%20newSS.rel='stylesheet';%20newSS.href='data:text/css,'+escape(styles);%20document.getElementsByTagName("head")[0].appendChild(newSS);%20}%20})();

It has always worked fine on previous Firefox versions. I have this script saved as a favorite in the bookmarks, but you have to manually click on it every time to make it work. Any ideas how to make this script run in Greasemonkey? It appears to be installed correctly the best I can tell.

Thanks.

 

I don't know which version of Windows you're running but, I'm visually impaired as well and I need everything in white on black in order to be able to read it. I accomplished this in Vista and Win 8.1 using Ease of Access in Control Panel. I've also got Win XP set for High Contrast white on black. I have not needed any type of script to get FF, IE or any window or folder to show in high contrast. I've tried high contrast in Win 10 TP but, apparently, it's not fully implemented in Win 10 yet