The Modern Browser Landscape
In 2021, there are three types of browsers that dominate the market. These are Chromium based browsers which use Blink, such as Google Chrome and Microsoft Edge, the Webkit based browser Safari, and Mozilla Firefox, which uses a Quantum browser engine. The most used browsers in the world today are Google Chrome with over 70%, Safari, Firefox and Edge.
While I probably didn’t need to tell you all of that, it sets a good foundation for understanding where the focus is for browsers. Nowadays, most websites and web apps aim to be compatible with chromium based browsers as they hold the majority share in the market. Due to this, compatibility with Safari and Mozilla Firefox could be seen as a secondary priority. The underlying web rendering engines and processes are different, so extensions work differently between these types.
Safari, even though its share is relatively limited, is absolutely dominant in the Apple ecosystem so developers aiming to target Apple users must account for them using the Safari browser. This is not the case with Firefox, as there is no system in which it is dominant, except perhaps GNU/Linux and its various distros as it comes preinstalled. Even then, some users opt to install another browser such as Google Chrome.
The Modern Extension Landscape
Extensions must be developed and then brought into the different browser markets via the Chrome Web Store for Chromium browsers, the Firefox Add-Ons store for Mozilla Firefox, and the App Store for Safari.
These extension stores all have different categories for finding applications to help you streamline your browsing experience, whether that be managing your documents, blocking adds, or some other use case. Extensions are most common on the the Chrome Web Store, but usually each extension has at least a Firefox counterpart.