@bartavi
OK, so in Unicode you have these special characters\*, combining characters. When you put a combining character after another character, it alters it. For example, U+0301 "COMBINING ACUTE ACCENT" ( ́) will put an accent on the previous character (like é).
\*not "special characters" as in "printing chars" vs "special chars" special characters, if you're familiar with that.
[1/]
@bartavi
There are some characters, the regional indicator letter characters, which act like combining characters. Here's U+1F1E6 "REGIONAL INDICATOR SYMBOL LETTER A": 🇦
When you type them next to eachother, you'll get a flag. Here's U followed by S: 
Your computer probably displayed that as the US flag.
I did some research and the flags in the titlebar are of the codes VE, GB, and VE. The flags in the tab in Firefox are of the codes UA, ??, and UA, where ?? is a flag I don't recognize. [2/]
@bartavi So I don't know exactly what happened; there may be a glitch with long sequences of regional indicator symbols. VE, GB, VE is likely just "VEGBVE" and may be confusing what's interpreting them. Maybe there are multiple sequences of regional indicators that indicate the given countries? Sorry I can't help more. [3/3]
@bartavi But while we're on the topic of Firefox, they added a TOS and are setting up to sell your data. Look at the #Firefox hashtag -- it's bad.
https://youtu.be/E4JOnQY_qbo