Usually Mozilla Firefox saves all the bookmarks in a SQLite database file so that you can access it easily and do any kind of changes you need. For doing this you will have to follow these steps.
First you will have to install SQLite Database Browser and enter this command
If you don’t have SQLite Database Browser , simply download and install it from SourceForge. Before doing all these don’t forget to backup your bookmarks OR you will lose everything if anything goes wrong. Then you will have to close Firefox as you won’t be able to edit bookmarks in it is running mode. Now run SQLite Database Browser and then you will have to open places.sqlite file which you will find in your profile folder.
apt-get install sqlitebrowser
After all this, just run the below SQL so that it will remove all the description of your bookmarks.
Now you just have to save and close it. Now start your Firefox and it is done.
delete from moz_items_annos where anno_attribute_id = 2