A further update – the digitised file viewer in RecordSearch doesn’t have the same session problems, so you can share a link to the digitised file without problems. For example this link:
https://recordsearch.naa.gov.au/SearchNRetrieve/Interface/ViewImage.aspx?B=149309
But what if you want to share a link to a particular page of a digitised file? When you click on the Next button in the digitised file viewer you’ll notice that the url itself doesn’t change, so sharing the url will just take you to the front page. But you can add an extra S parameter to set the page number. For example, to go to page 3 of the file above:
https://recordsearch.naa.gov.au/SearchNRetrieve/Interface/ViewImage.aspx?B=149309&S=3
Once again, if you use the Zotero translator for RecordSearch it will create this link automatically.