Yes, in the strictest sense both browsers may rely on public open source libraries, which means they have some shared code, but they do not share any code directly with each other (e.g. Chrome is not a dependency of Firefox, Firefox is not a dependency of Chrome). I see this as not equating to "code sharing" because they both happen to use a library. Ironically for other apps that'd usually be something like OpenSSL, but in the case of Firefox and Chrome they actually have entirely separate TLS codebases as well (NSS for Firefox and BoringSSL for Chrome).
For some of these shared open source libraries, either Mozilla or Google is the primary contributor/maintainer, and both organizations usually make contributions. This is true across many things, even libraries in the open source space that are not involved in the browsers themselves but may be in the toolchain (Mozilla has produced robust open source CI/CD tooling, bug trackers, etc over its history).
For some of these shared open source libraries, either Mozilla or Google is the primary contributor/maintainer, and both organizations usually make contributions. This is true across many things, even libraries in the open source space that are not involved in the browsers themselves but may be in the toolchain (Mozilla has produced robust open source CI/CD tooling, bug trackers, etc over its history).