We have automated tests in place, running against PHP 5.3, 5.4, 5.5 and 5.6, to make sure this will never happen. Nevertheless I did try it manually myself just now against a Joomla! 3.4.3 site running on PHP 5.4. I can confirm it works fine.
Check that the System - Admin Tools plugin is published and is the first plugin to load (it's at the top of the list when ordered by Ordering ascending).
Go to Components, Admin Tools and make sure there is no big red box telling you that the installation is corrupt. Do note that the check may take a few seconds to complete so please do stay on the page for a minute or so to be sure there is no big red box after all. If you do see this big red box please install the component, twice in a row, without uninstalling Admin Tools before or in between.
Go to Components, Admin Tools, Web Application Firewall and make sure the correct IPs are set in the IP whitelist feature.
Go to Components, Admin Tools, Web Application Firewall, Configure WAF and make sure that the "Allow administrator access only to IPs in Whitelist" option is set to Yes. Please note that if you don't do that the whitelisted IPs are IGNORED per our documentation.
Go to Components, Admin Tools, Web Application Firewall, Configure WAF and check the Never block these IPs and Whitelisted domains. If your IP or its domain are in these lists they are NOT subject to any security checks, including IP whitelisting.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!