"since 2 Versions", but which version are you using now? :) Do you mean the lat 2 daily builds? Some of the problems which might cause material editor/browser to get slow have already been fixed so this shouldn't happen in theory.
Is the material/map browser slow even in new, empty scenes, or if you close all the custom libraries?
Could you send us any of the custom libraries that might be slowing down the browser, if not publicly, then to support@corona-renderer.com ? (would be great if these were small files)