Looking at Firefox ftp sites I see one is:

Dir pt-BR/ Dir pt-PT/

Did you download the correct version language? I think BR means Brazilian. This is the 64bit version. Beyond that you should be able to add language module to your Firefox.

https://archive.mozilla.org/pub/firefox/releases/133.0/win64/pt-BR/

https://archive.mozilla.org/pub/firefox/releases/133.0/win64/pt-PT/

Although listed as one of the options for default language, the current version of Firefox, which is my default browser, does not accept Brazilian Portuguese as the default language. It only accepts the Portuguese version, from Portugal which, to me, who speak Brazilian Portuguese, with all due respect, is a pain in the butt. I have tried, dozens of times, to delete the Portuguese version and set the Brazilian version as the default language. It works until I shut down the computer. The next time I turn on the computer, to my eternal dismay, Firefox cancels my previous language setting and reverts itself to the damn Portuguese version, which I dislike to the extreme.So I am, hereby, taking the issue to you with high hopes that this abdomally be straightened out once and forever. Many heartfelt thanks and wishing you sucess. Damião

Download Portuguese (Brazilian) - Português (do Brasil) version from https://www.mozilla.org/firefox/all/desktop-release/win64/pt-BR/ as it is in the list at https://www.mozilla.org/firefox/all/desktop-release/win64/

If you download Firefox from another mozilla.org page it may be going by your IP location and guessing what you need.