Mozilla (Suite) was similar to Netscape Commumicator and included browser, mail, webpage editor and maybe other functions as well. I don’t recall you could install the components separately. Later they decided to release a standalone browser (Phoenix/Firebird/Firefox) and then mail client (Thunderbird). IIRC they had standalone calendar (Sunbird) and webpage editor as well. Eventually they discontinued Mozilla and the closet thing would be the community-maintained Seamonkey.

IIRC they switched to webextensions in Firefox 57 in 2017. Even before that it was never the browser with the biggest market share, and Chrome had already got a huge market share in 2017.

I’ve been using Phoenix/Firebird/Firefox as my default browser since 2003. Never understood the appeal of Chrome.