You may experience lately the impossibility to save your product files on your PrestaShop store the first time. You start to get annoyed by analyzing the logs, by activating the debug mode without success.
Please note that the problem does not come from your store directly but from the latest update of your Firefox browser. This one makes incompatible the transmission of the data under certain forms and thus prevents a suitable recording of your product sheets.
PrestaShop has fixed this problem on version 22.214.171.124 so you have several possibilities.
If you wish, you can update your 1.6 installation to the latest version available to date to correct this problem.
Remember that for any update, you must perform a first test on a copy of your site. Rather on the same server as locally to be in the same configuration.
Don't forget to make full backups manually and especially know how to restore them in case of problems.
If you don't know how to do this, you can contact me directly on my PrestaToolBox website.
Integrate the correction
You can find the corrections to be made on 9 files of your installation directly on the Github site.
In red the lines to be deleted and in green those to be added.
If you don't know how to do it or if you are afraid to implement this fix, feel free to order a ticket and I will take care of everything.
Update May 14, 2019
For Thirtybees users
The thirtybees team proposes a patch directly in their GitHub repository. 3 commits are to be implemented: