How are you changing the input language ? Is that via a keyboard shortcut or via some OS language selector ?

Keyboard shortcut. I googled this problem and I was led to this topic https://www.linuxquestions.org/questions/linux-newbie-8/%5Bmint%5D-firefox-has-a-different-keyboard-layout-than-the-os-itself-4175644537/. That guy had the same problem as I, but there is no solution. And one more thing, switching language works file only after I go to the gnome settings/region and language and change my input sources priority. In that topic somebody proposed to write a script that does it every boot, but I dont think that it's a proper way of solving this problem. Off topic. I'm newbie in linux, so my answers aren't absolutely correct.

I only use the en-US keyboard layout and if necessary I use the compose key for special (accented) characters.

• https://en.wikipedia.org/wiki/Compose_key
• https://fsymbols.com/keyboard/linux/compose/

Well... I use cyrillic writing script, so it's not my case. ADDED. After some research, I've understood that problem is in my profile.