if your experience intermittend connection try to check your network cable, or the ISP provider, Second is go to run command, then type cmd press enter from there type ping www.google.com -t then press enter if the message shows reply from ......... bytes ........ meaning you have an internet connection, may be your firefox browser is infected by a malware or virus clear all the cache, history, then try again. If the above mention is not working try to uninstall the browser and install back... hope it works...