see this answer https://support.mozilla.org/en-US/questions/1080834#answer-774566

Used 3rd way with manual import export - didnt work , I think visual bookmarks doesnt support import export , But I remember couple years sync work perfectly even thru internet (transfered all day easely)

roloTomasi said

imported bookmarks from one pc win 10 to another pc win 10 everything imported except visual bookmarks ,in settings all 6 checkboxes on

Are you referring to the Favicon images for your bookmarks?

If so, synchronizing Favicons isn't part of what Sync does. Those images will get picked up by the "receiving" Firefox installation as each of those bookmarks are used for the first time.

tl;dr comments The Favicon image data is huge when added to the URL for the respective bookmark; the ratio was about 20:1 by my estimation when working with bookmarks files in the mid-00's. IOW, including those images migh have approached 20 times (or more) the amount of data being transferred on an initial Sync with a new device. Not a big deal when Sync updates each device daily using Sync, but depending upon how large a bookmarks collection it could have caused immense issues for users.

I have seen mention by user's in this forum about having only a hundred or so saved bookmarks, while other user's have mentioned having 50,000 or more saved bookmarks. Mozilla needs to take that vast difference into consideration when writing code for Firefox and related services.

While Firefox over 10 years ago on a somewhat dated PC, I was having a problem with having just 2000 bookmarks in Firefox; where Firefox was very slow and it got worse as more and more websites began using Favicon images and/or started using "larger" (file size) Favicon images. When I programmatically "stripped out " those images and discovered how much "load" those images placed upon Firefox - it "flew" unbelievably fast even when I imported my entire bookmarks collection 10 times to make it 11 times as large as it started out. When I did that 10 more times, I started seeing the slow down that I had been having with those images saved in Firefox. Non-scientific for sure, but it told me what impact those Favicon images had in that era of Firefox development and PC hardware for user's with "dated" hardware. (1999 PC which was "state of the art" when new, and in 2005 with Firefox 1.5)

When Sync was being created back in 2007-08 the decision to not include the Favicon data in the Sync process, probably to allow Sync to work at reasonable speeds for data transfer when Firefox users were stuck on a dial-up or slow DSL connection.

That all said, with recent changes to how those Favicon images are stored inside Firefox in a remote file outside the main places,sqlite file, it is possible that the developers might be able to add the Favicon data to the Sync process and Sync server data load. As a non-programmer type, I think that the Favicon data could be sync'd after the initial Sync on newly connected devices slowly over a few Sync connection events, depending upon how many bookmarks the user has in Sync, the "current" load on the Sync server clusters, speed of the user's connection, and other factors.

try this add-on https://addons.mozilla.org/en-US/firefox/addon/onlinezakladki/

When open blank tab there screen with bookmarks - I need them to import