Facebook implements heavy image compression, resizing, and formatting for photos to enable its pages to load faster and save bandwidth and storage. This applies to all photos uploaded to Facebook, no matter what software you are using.
We’ve tested this using different software (including a direct upload from Facebook, Social Marketing, and other popular social media tools.) The photo was displayed with the same reduced quality on all of the software we tested, confirming that Facebook is responsible for the photo quality and not Social Marketing.
To ensure that your photos display in the highest quality possible, Facebook recommends a size of 2048 pixels wide or smaller and saving your image as a JPEG with an sRGB color profile.