I believe this option on the "Addon:Themes"
- Fixed Scrollbar (Requires Restart) This changes the Gramps scrollbars to be a bit more 'classic' in that they don't disappear, they have the up/down buttons at the ends, and clicking in the empty space above and below the slider acts as page up or page down. This is deselected by default. This setting is only visible on Windows machines. Note that changing this setting requires restarting Gramps, and may require restarting your session (Log off and log back on to Windows), particularly when disabling the setting.
is not there anymore. at least i can not see it on my version ( please look at the screenshot on the Hebrew page)
The checkbox still exists in the version 0.0.9 of ThemesPrefs plugin. (Version found via Info using "Plugin Manager - Enhanced".) Which version do you have installed?
I wonder if the Right-to-Left orientation violates the parameter options?