Firefox hide native vertical tab bar if Sidebery is enabled

userChrome.css

/*
Credit: https://gist.github.com/abhinav/00c2053b750b72e2d43bcf1652b5fb66
This is a userChrome.css for Firefox
that hides the vertical tab sidebar (used by Sidebery),
but only if Sidebery is enabled and the window title contains the "sidebery" preface.

Instructions:
1. Enable userChrome.css support and vertical tabs in Firefox:
    1.1 Go to about:config
    1.2 Set `toolkit.legacyUserProfileCustomizations.stylesheets` to `true`
    1.3 Set `sidebar.verticalTabs` to `true` (this enables vertical tabs support)

2. Enable Sidebery window title preface:
    2.1 Open Sidebery settings
    2.2 Navigate to *Help*
    2.3 Set the *Preface value* to `sidebery`
        and enable *Add preface to the browser window's title*

3. Create or update userChrome.css:
    3.1 Open Firefox menu → Help → More Troubleshooting Information
    3.2 Scroll to *Profile Folder* and open it
    3.3 Inside the profile folder, create a `chrome` directory (if it doesn't exist)
    3.4 Inside `chrome`, create or edit `userChrome.css`
    3.5 Paste the following CSS

4. Restart Firefox

Note: This assumes vertical tabs are enabled in Firefox.
*/

#main-window[titlepreface*="sidebery"] #sidebar-main {
  display: none !important;
}