As far as bookmarks from 1995 goes, I doubt if the 'age' is considered from way back then. Firefox got a new bookmarks storage system with Firefox 3.0 in June 2008 (places.sqlite) that was a major departure from what Netscape and the original Mozilla Suite used; which Firefox which was named Phoenix at the beginning and then was re-branded as Firebird for a short time before becoming Firefox in 2004. So 2008 should be considered the "base" date of the current bookmarks system.

There is no "master" device with Sync, the synchronization of bookmarks is equal - save for "mobile" bookmarks (Firefox for Android and Firefox for iOS devices). The Sync server will know the 'age' of each bookmark, but there are no user controls for Sync beyond whether a data category is toggled on for inclusion in the synchronization process and whether Sync is Connected or Disconnected.

The situation on "mobile" categorizes or sets into separate folder displays per device the bookmarks that originate on "mobile" devices. An arrangement that is controversial with some users.

That said, the initial synchronization of multiple devices for a new Firefox Account (FxA) may take a seemingly unreasonable amount of time; some reports of multiple days of use of Firefox on each device before the process seems to be completed. BUT, that could have been due to the user getting frustrated and that user rearranging bookmarks manually per device in an attempt to "fix" what they didn't like which only exacerbated the issue.

Best use tip: When manually rearranging bookmarks 'Disconnect' from the Firefox Account; then 'Connect' back to the FxA system to allow for synchronization of the "batch" of changes in one connection.

I have been using databases Dataman/dBase/SQL and various online data bases since 1969. When you update a field you have to instruct/program/code the software which field to update and from which database/table and under what conditions

If there is a date field in the record the newest date is assumed to be the newest information. Some of your coders must be able to read the code and tell me the conditions used for the update to the data record/row/id/field?

As far as have bookmarks from Netscape 1.0 read the History of Netscape and Firefox and you will see how they where intertwined. The first browser I used was and add-on to Microsoft Word in 1995 a few months before I signed up with a paid Internet Provider in June. I was using a free-net before that.

I am quite aware of the relationship between the Netscape bookmarks.html format and Mozilla.

The Mozilla Developer Network (MDN) contains the documentaton for all of Firefox, including the "Places" database. https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Places/Database