ableton has a seperate folder for your third party vst plugins. usually you tell the app where that folder on your system is via preferences on first start up. but if you didn't change the default installation path, it recognizes them automatically on mac and windows i think.
the audio effects, midi effects and instruments folder and in live 9 the whole other browser tabs like sounds, samples etc. are just for live's own stuff and things you install as so called packs.
like fistikuffs said, you have to go to the plug-ins tab in live's browser. should it be not inside there, first do a rescan of your plugins.
you can do this via preferences, file/folder and nearly bottom there is a section where you manage your third party plugins and change path, make a new scan etc.
all the best