I mentioned this below, but check to see what your history limits are in Firefox (https://support.mozilla.org/en-US/questions/1039372). It's possible if you do enough browsing that you might have trouble finding older pages because they're not there anymore.
I'm not sure what the best mitigation is for that, I've kind of accepted that history for Firefox is short-term, not long-term. It might be possible to rig up a webextension to save history more permanently, but I suspect it would need to do native messaging I think to do that, and at that point maybe it's better to just do regular copies of the SQLite database.
Relying on Firefox history less also has the kind of minor advantage of allowing you to be more aggressive about cleaning it yourself, which can have a noticeable performance impact in some cases.