Please explain more completely.

Specifically, what type of format are you using for "saving bookmarks to a file"?

Are you doing export in bookmarks.html format? https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Or are you dealing with a JSON / JSONLZ4 format file? the bookmarksbackup format that Firefox uses to automatically backup the users bookmarks https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

Both exporting as an HTML file or using the backup option to generate a JSON file should preserve the icons for your bookmarks.

However, simply copying the places.sqlite file from your Firefox profile folder will not. The favicons.sqlite file holds that data.

export in bookmarks.html has always included the favicon data (website images).

View the saved bookmarks.html file and "search" for ICON.

This is the tag for that data ICON="data:image/png;base64, .......................... very long string of alpha/numeric data for each favicon that is present. And that data takes up a lot of room - like well over 10 times as much data as the URL and 'name' for each bookmark.

Yes, exactly. When exporting Firefox bookmarks to a html-file is it so that saving time to time, some or much small icons are missing, if I´m reimporting and opening my bookmarks.

Greets

Dear Firefox team, please fix that all icons from Firefox bookmarks will be saved into exported html file. Thanks in advance.

If you want to file a bug report about this so that the developers can look into the issue, you can do so on Bugzilla.