I'm pretty sure Chrome, at least, doesn't support SOCKS yet at all.
I was trying to make a shell script just the other day that would set up a SSH SOCKS proxy to a remote box and launch a browser using it, but couldn't do it from the command line in either Firefox or Chrome (didn't try a custom profile). Furthermore, I couldn't get it working in Chrome at all (shame; Firefox is more sluggish, and Opera won't even start on my box).
One problem with Chrome is that its proxy config interface really is just interfacing with the GNOME desktop-wide proxy settings. So it's impossible to have Chrome use multiple proxies or to only have one instance of Chrome use a proxy, but another instance not -- even if both instances have completely separate user data directories -- and all proxy changes are instantaneous across all Chrome instances. (At least for Chromium 5.0.391.0 on Linux)
Chrome on OS X can use SOCKS, but not explicitly for Chrome, since the operating system manages the connections under System Preferences > Network > Advanced > Proxies.
I was trying to make a shell script just the other day that would set up a SSH SOCKS proxy to a remote box and launch a browser using it, but couldn't do it from the command line in either Firefox or Chrome (didn't try a custom profile). Furthermore, I couldn't get it working in Chrome at all (shame; Firefox is more sluggish, and Opera won't even start on my box).