A New Firefox 53.0.3 will be released later today 19 May 2017 to get when released click on help>about Firefox>check for updates Release notes
fixed
-
Fix hangs when using a proxy with NTLM authentication (bug 1360574)
-
Fix excessive resource usage from the captive portal detection service (bug 1359697)
https://www.mozilla.org/en-US/firefox/53.0.3/releasenotes/