Hello Giorgio, can you open an issue on https://github.com/aaFn/Bookmark-search-plus-2/issues with details of your Firefox version and conditions ?
The only case where it shouldn't work is with Firefox 56, because that Firefox version does not support the sidebar show/hide actions.

Thank you, aaFn.
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Ok, glad it's resolved. Thank you for coming back here to say.
aaFn.