Earlier quoted context omitted.
The journalists definitely got their facts wrong here, but they missed the overarching story. Why is Mozilla acting like a tech company/startup, and not as a non-profit here to push Firefox and other projects under their management to new heights? Mozilla has basically ignored Firefox for the past few years and let it languish as a single threaded browser in a multi-threaded world, where the other 3 major competitors…
Electrolysis? Servo? Rust? I'm far from an expert, but the switch to multithreading has been perilous to not break everyone's favourite plugins, likewise the switch from XUL Electrolysis is basically here and working, slowly rolling out
Unless you use extensions, which used to be one of Firefox's biggest advantages.
I gave Firefox on Ubuntu a try for a week last month because I was looking for a replacement for Chrome and if I wasn't tech savvy I wouldn't have been able to figure out that Firefox was running in single-process mode and how to fix that.
E.g. the default "Ubuntu integration" extension that Firefox ships with on Ubuntu (where it is the default browser) is not compatible with electrolysis. Additionally the (now outdated) Lastpass extension from the Firefox addon shop isn't compatible. I think the Trello Scrum extension also isn't compatible. The React developer tools also only just experimentally enabled compatibility.
I'm not nitpicking -- users don't care why Firefox is slow or why electrolysis is disabled. If an extension is available for Firefox, especially if it's available on the official addon shop, users expect it to work and not to make Firefox slow to a crawl.
That said, even with multiprocess mode I found that Firefox would often be considerably slower when having many tabs open (it's normal for me to keep 30-40 tabs open and this isn't rare, even among my non-developer friends). And as a developer the dev tools are still lightyears behind.