Read MARC records
When a web page contains a MARC record, easily identifiable by being inside a <pre> element, with no intervening tags of any kind, I would expect the "Create New Item from Current Page" button to use that MARC record. It does not.
OTOH, I guess the fact that Zotero cannot know from just the URL that there is a MARC record on the screen (except via the never-ending whack-a-mole game of adding yet another translator/URL match) does impose some constraints on the solution.
So I'll frame the problem like this: it should *always* be possible to punch a button to make Zotero use a plain-text MARC record that is displayed on the current web page. Simple things should be simple.
As I say on the ticket, ideal would probably be some sort of meta translator that runs on every page and does a regex for supported import formats and passes the content off to the appropriate format translator(s).
Since such a translator would have to run a complex regex on every page, this would need to be profiled to make sure there wasn't a performance hit.