Rails website speed seems low

Hi I am Ruby on Rails beginner,Our Rails application is hosted in amazon web services. For last one week our website is taking long time to respond. This happens only in a particular browser that means if site slow in Firefox and if I go to chrome in same system it works well and vice verse.I don't know where are the places to look up to solve the issue. Please suggest me the way to find and rectify the problem causing places.