See this bug report for some information:

• bug 985930 - History older than 6 months is not synced

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https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

Well that just sucks what's the whole point of Firefox Sync then. Utterly useless looks like I'm deleting my account. Thanks for the info.

The history can be quite large, normally around 100,000 pages as you can see in the places.history.expiration.transient_current_max_pages pref on the about:config page. It would take quite some time and a lot of storage space on the Sync server and it would affect Firefox's performance to sync that much data. That is why the amount of history that is shared is limited. You could copy the places.sqlite file to other devices to have all the history and if necessary restore the bookmarks from compressed .jsonlz4 backup.

So I've been to busy to respond but I would like to know how would copying the places.sqlite file to other devices will allow me to have all the history? Wouldn't that just be the same problem? A little explanation on this would be helpful.

Yes, copying the places.sqlite file to the Firefox profile folder of other devices should copy the bookmarks and history. Make sure to remove possible existing places.sqlite-shm and places.sqlite-wal files. If you need to keep bookmarks then export the bookmarks to an HTML file to be able to import this HTML file afterward and merge these bookmarks.