When a PDF author creates "bookmarks" or hyperlinks in a PDF, they can store a custom zoom level in the bookmark/link rather than simply inheriting whatever level the user has chosen. I don't know whether the following hack really is working for me or I just imagine it, but you could give it a try:
(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
More info on about:config: Configuration Editor for Firefox. Please keep in mind that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.
(B) In the search box in the page, type or paste pdfjs.ignoreDestinationZoom and pause while the list is filtered
Firefox should show a bar with Boolean Number String and + button
(C) Keep the selection on Boolean and click the + button to add a new true/false preference
(D) If Firefox does not automatically set the value to true, double-click the preference (or click the toggle button toward the right end of the row) to switch the value to true
Note that any PDF you already loaded needs to be reloaded (Ctrl+R) to reflect this change.
Any luck?
