I highly recommend using Chrome's multiple user feature to log into your separate gmail accounts. This is the only thing that has kept me sane at the last couple companies where we used Google Apps.
Run it with the following command-line arguments: -ProfileManager -new-instance
That brings up a profile picker/creater. Each profile is isolated, different plugins, different cookies, etc. The only information leakage is when a plugin keeps its own data outside of the profile directory, like Adobe Flash keeps its version of cookies in a per-user directory rather than a per-profile directory.