This is only due to the failure (and unwillingness) of Mozilla to build a truly modular, expandable browser.
Mozilla isn't even trying to compete with Google anymore at this point. They are only implementing new features into Firefox that Google has first built into Chrome (and firing developers working on features that could actually set Firefox apart from Chrome). Also, they are quick to implement most "features" Google implements, no matter how user-unfriendly it may be.
An example for this is Mozilla implementing Manifest V3:
https://www.eff.org/deeplinks/2021/11/manifest-v3-open-web-p...