Your settings for the browser add-on, including whether it is hidden or not, should be retained between each visit to Gmail. Aside from clicking the small arrow to reveal the add-on, there's nothing further that you need to do to save this setting.
It's possible that a browser issue is preventing the add-on from saving its settings. If you haven't done so already, would it be possible to try clearing your browser's cache and cookies, restarting the browser, and trying again? You can read more about clearing your cache here.
Hope that helps!
Posted 3 years ago