Is the feature relevant to the Firefox PDF Viewer?
Yes
Feature description
Currently, Firefox does not remember last view position/page, Which I suppose because of this PR (#4559). Also there is an option in about:config (pdfjs.historyUpdateUrl) which seems to be save position but only for web links. It would be nice add this option at least only for local pdf files in Firefox pdfjs.
Other PDF viewers
This default to many PDF viewers.