Creating Javascript is not something to be proud of.
Either way, Firefox's decline has nothing to do with him. It's because Chrome is good. I know, Google steals all your data, but most people just want a browser that is fast and easy to use. If they care about privacy, there are numerous forks to choose from.
I use Firefox, but the compatibility issues and long standing bugs are frustrating. Most people would probably give up, and even I look at new Chrome based browsers to see if moving back is feasible now and then. I think the lack of uBlock on Chrome will probably keep me here, but I'm far from a typical user.