Support for arm64

[MrCyjaneK]

Currently when trying to run ./build the script exits:

x@arm64host  /Software/i2pdbrowser/linux/build   master  ./build 
This script is preparing firefox 91.12.0esr for use with I2Pd
Downloading firefox...
curl: (22) The requested URL returned error: 404                                                         

[TRY 2] I'll try downloading Firefox with shorter language code
curl: (22) The requested URL returned error: 404                                                         

[TRY 3] I'll try downloading Firefox with the English language code
curl: (22) The requested URL returned error: 404                                                         

[Error] Can't download file. Check your internet connectivity.

I'm 100% sure that it is because of https://ftp.mozilla.org/pub/firefox/releases/91.12.0esr not having a Linux-arm64 release available for download. Can we fallback to compiling firefox from source or using already installed firefox or that is that not an option?

[r4sas]

This can be done, but I don't know if separated profile directory would work correctly in that case...