HoYoverse CodeEnter is a Firefox and Chromium browser extension that allows you to enter codes for the HoYoverse games, earning rewards for doing so. You can also automatically get rewards for daily marks in HoyoLab by logging in here(Genshin) or here(Star Rail)
Install extension from the Firefox add-on store.
I have no idea how to publish extensions to the Chrome Store
Chromium: you will have to log in to your account through the extension, at least for me.
Firefox: just login to your account.
Click on the extension icon, enter the promotional code, you can also share it with friends, a site with a promotional offer will open in a pop-up window where you can select the account region and enter the promotional code in one button.
From 2.1.0 the function of automatic collection of daily rewards is available! Check your in-game mail and claim your rewards!
I just sometimes had to enter promo codes both ways, and with my number of extensions, it was problematic to find the right one... The extension is partially based on my past extension Genshin CodeEnter(why not HSR? it is itself based on Genshin).