A user on the Zotero forms recently reported a processor failure in LibreOffice when a setting is changed to per-page footnote numbering. The error was triggered by input validation code that I added to the processor a couple of months ago, which requires note numbers fed to the processor to be sequential. Zotero have circumvented the error in the latest LibreOffice plugin by reporting out the document index of footnotes to properties.noteIndex in citation input. That will work, but the value of first-reference-note-number will no longer be aligned with note numbers.
There isn’t any way to handle this use case properly in CSL 1.0.1, and I won’t be doing anything to extend citeproc-js to cope with it. I just mention it as a general development issue for the time when the CSL schema comes to be revised.