No need for IE, just paste it to notepad first than cut & paste it from there to the translation web page.
Notepad "cleans" most junk you paste into it into pure text.
I use Firefox too so I'm keeping an open Notebook Window to follow the dialogue here ;-)
You can click on the "Al Bhed or code" box and enter your own codes too, i.e. , type 12345 and it will translate abcde letters a = 1, b = 2,... All 52 upper and lower case letters can be numbers, asterisks, etc...
Another trick is to do double Al Bhed:
Ra ec cu lida (Rikku says of Vidina, meaning He is so cute )
gets turned into
Ny al li mety
If you click "English to code" again instead of "Code to English"