I have found the solution. In my opinion, the easiest way is:
Let's say you have 100 bookmarks in Mozilla and 4 more files with bookmarks in json/html format.
The idea is to have every file in html. So, export the ones in mozilla to html. Delete them from mozilla afterwards. Show all bookmarks -> Import and backup -> Restore -> Choose file -> choose one of the json ones you have(if you don t have any, skip this step). After that, export the newly acquired bookmarks to html and delete them from Mozilla. Repeat as many times as needed.
Now, you only have .html bookmarks, a few files. Make sure all the bookmarks from within Mozilla are deleted and start importing the html(Import bookmarks from HTML).
Do this for every html file, do not delete anything. After that, simply arange them, you will have multiple folders inside the bookmars but it shouldn t take more than 5 minutes and manually delete the duplicates after sorting them by name. And voila, no software, no bookmarks lost, everything takes tops 15 minutes (and I had hunderts of bookmarks in 5 different html files).