Thank you for opening a topic. First of all, any use of external javascript is causing a website to slow down. Facebook Page Promoter Lightbox is also using external javascript. The main cause of speed loss is blocking javascipt in the header. The main advice to mitigate those effects is by using a plugin that moves javascript to the footer and/or combines it.
Becarefull using these plugins, as there is many potential for conflict. Some plugins do not support footer loading due the way they are designed and some minification plugins don’t do a good job (forexample, they do not take into account relative nature of urls specified in css).
Also make sure,the speed google reports does often not correspond with the actual speed users are experiencing (due to elements loading in the footer for example).
