When Firefox is installed and it detects system language/region to be Lithuanian, it automatically sets webpage language list to: Lithuanian, Russian, Polish, English (United States), English. I install Firefox on clients' computers on a daily basis and I have to constantly remove or at least lower priority of Russian and Polish languages. Frankly, it has no right being so. While there are Russian and Polish minorities in Lithuania, for vast majority of users these languages are not relevant and for some that assumption can even feel disrespectful due to political and historical nuances.
Please leave English option as second by default. If user expects Russian or Polish, they would most likely have those languages applied system-wide anyways.