3.1.8

   * Optimize internal operations for better performance and less memory usage. (Some ideas are contributed by bb010g. Thanks!)
   * Become more safe to accidental recursive references of tree structures.
   * Reopen same site tab with the container inherited from the current tab correctly, when the tab is opened as a child of the current the.
   * Don't apply special new tab behaviors (ex. auto-attach to the current tab) to restored single tabs.
   * Don't apply special new tab behaviors for Ctrl-T or other commands, to tabs opened with URL (ex. opened from bookmarks or the location bar), even if the `about:blank` is choses for the default page of new tabs.
   * Don't invert children order for a restored parent tab.
   * Apply custom behavior of closed parent tab correctly when a parent tab is closed as a solo tab by an action inside the sidebar.
   * Accept dragged tabs from another Firefox instance as URLs.
   * Treat a tab dragged from the native tab bar to the sidebar as is instead of as a URL string, if possible. (You can deactivate this new behavior with setting `guessDraggedNativeTabs` to `false`.)
   * Refresh indent level of tabs detached from a window by drag and drop correctly.
   * Update visibility of the scrollbar when tabs are shown or hidden, for better compatibility with other addons like the [Simple Tab Groups](https://addons.mozilla.org/firefox/addon/simple-tab-groups/).
   * Brush up appearance of some UI elements in the options page.
   * Restructure some options under the "New Tabs Behavior" section for better findability.
   * URL like `ext+treestyletab:group?(title)` is available to open a group tab with specific title.
   * Show text-shadow with correct color for better readability of text with non-default theme.
   * Update `de` locale by SammysHP. Thanks!
   * Update `fr` locale by ariasuni (and DarckCrystale.) Thanks!
   * Update `ru` locale by wvxwxvw. Thanks!