日本語じゃないと困るって人向け
どちらもPale Moon 27.4.0で動くのを確認

LP 27.5.0_RC1
https://github.com/JustOff/pale-moon-localization/releases/download/27.5.0_RC1/ja.xpi
LP 27.4.0_RC7
https://github.com/JustOff/pale-moon-localization/releases/download/27.4.0_RC7/ja.xpi