Bookmarks-Favorites reset on their own

Without any useful information it's impossible to tell. Please do the following:

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate towww.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community It is helpful to us if you download the report to your Desktop.

Your EtreCheck report shows nothing wrong. Your bookmarks are gone and simply need to be rebuilt. Operating with a backup would have solved the problem in seconds! This time you were lucky it was only bookmarks, next time you may lose data that is irreplaceable like photos, music collections, etc.

Before you do ANYTHING start using Time Machine!!! It only requires and external HD, many experienced users on these forums like the OWC Mercury Elite Pro at www.macsales.com. Why, HIGH quality, reasonable prices, and great support.

Did you try to recover from your TM backup?:

~Library/Safari/bookmarks.plist