As of 2021 Adobe has ended support for the Flash Player plugin and it is removed in browsers (refer to Saying goodbye to Flash in Chrome for details).
Magento 1 Image Uploader depended on Flash. With flash plugin removed product image upload on Catalog > Products is now broken in Chrome and Firefox.
There is official patch from Magento to overcome this issue in Magento 1.9.x and all older versions, SUPEE-8788. It comes along with other security fixes and replace old Flash uploader with native HTML5 uploader supported in all modern browsers.
To install SUPEE-8788 you can refer to one of the following articles:
Posted in: Magento Maintenance