Before recovering old bookmarks, decide whether you want the old collection to replace the current one or sit alongside it. Firefox’s Restore and Import bookmarks from HTML options serve different purposes. Choosing the wrong operation can remove newer links you meant to keep.

Preserve the current collection

Open the Firefox menu, Bookmarks, then Manage bookmarks. In the Library, use Import and Backup to save a dated backup of the current collection before replacing anything. Give the file a name that distinguishes the current set from the older recovery file.

Inspect which links matter on each side. For example, the older backup may contain a complete project folder while the current browser contains several new supplier pages. Write down a few unique examples from both so that the eventual result can be checked.

Select the intended operation

Restore under Import and Backup lets you choose a dated automatic backup or a file. Mozilla warns that this replaces the current bookmark set. Use it only when replacement is the intended outcome and the current set has been preserved.

When the goal is to combine old and new bookmarks, use the HTML import route with an actual HTML bookmark export. Do not assume changing a filename’s extension converts a backup into another format. Keep the source file unchanged if Firefox cannot read it.

Afterwards, check the distinctive folders and recent links you listed. Avoid repeating an import just because an item is not immediately visible on the toolbar; inspect the Library first. Keep both dated copies until the collection is usable. Sync reflects ongoing changes and should not be treated as an independent historical bookmark archive.

Source: Mozilla Support.