147 packages don't strike me as that many, that's less than 1% of all Gentoo packages. I expected much more.
EDIT: And several of those packages are binaries. Apart from the *-bin packages, I've identified TeamSpeak, dev-libs/amdgpu-pro-opencl, Skype, and Slack. That leaves 138 packages.
(Sane) web UIs in general should be fine, since they can just use the browser's JS engine. I don't think transmission is affected, at least it's not listed as masked.
You're right about firefox though, which is weird. Apparently node is a build dependency, but I can't figure out if that's something specific to the ebuild (that Arch's PKGBUILD does as well) or just generally something the buildsystem requires, but it's not listed as a dependency at https://firefox-source-docs.mozilla.org/setup/linux_build.ht....
EDIT: And several of those packages are binaries. Apart from the *-bin packages, I've identified TeamSpeak, dev-libs/amdgpu-pro-opencl, Skype, and Slack. That leaves 138 packages.