Put the config settings in a user.js file and save it in the root directory of your Firefox profile. It should look something like this:

user_pref("always-show.config.setting", false);
user_pref("hide-sidebar.config.setting", true);

I removed sideberry once vertical tabs came along. Any reason to use it over the built in way?

i always just dragged the default sidebar all the way to the left to shrink it into a single row. it doesn't disappear but it at least stays out of the way