The additional features that you can add to Google’s Chrome browser, such as password managers, ad blockers, and so on are called extensions. Mozilla’s Firefox browser calls them add-ons and it is one of the features that made Firefox so popular back in the day due to the amount of customization and features it could potentially bring to the table.
That being said, it looks like Mozilla has decided to start adopting extensions similar to those used by Chrome and Opera. According to Mozilla (via TechCrunch), this is apparently done so that developing extensions across multiple browsers will be easier for developers, as opposed to developing the same tool but using different techniques.
Mozilla’s Kev Needham says, “We would like add-on development to be more like Web development: the same code should run in multiple browsers according to behavior set by standards, with comprehensive documentation available from multiple vendors.” To that extent, developers will apparently only need to tweak their code a bit in order to get their extensions up and running on Firefox.
Mozilla is also hoping that with the use of the WebExtensions API that it will allow them to cut down the amount of time needed to review extensions before approving them, with the aim to bring it down to five days. That being said with it being easier to develop for Firefox now, don’t be surprised if you start seeing more Chrome and Opera extensions appear for Firefox in the future.