no, its part of the 100% optional experimental features section of Firefox (now called Labs). Its always been there (since its existed in Firefox Nightly for years), you just had to enable the menu panel option with a configuration setting, but now it (the menu panel) is shown by default. It should be noted, with very few exceptions, none of the items in this menu were ever enabled by default, unless they were to test turning off features for suneset reasons or spec changes (i.e., SameSite cookie permission attributes).

To my knowledge, the chromium devs have said (and i am paraphrasing here) that maintaining such a large C++ codebase from a security standpoint is a figurative nightmare. I think they have only recently begun to start migrating some code to rust or other languages (i'm not 100% if they were also looking into Zig)

unfortunately, its based on c++... so could be a security nightmare unless they are very very careful :|