The original bug report:
Codepoints that cause the crash:
U+0C1C U+0C4D U+0C1E U+200C U+0C3E
Here is a pastebin with the glyph: https://pastebin.com/9Tr8ytTr
Warning: if you paste it into your address bar, it may crash Safari and cause it to crash again every time it shows up in your history after that. If you paste it into other apps, they may or may not crash (many iOS apps confirmed and iMessage, Terminal, and others on MacOS).
This is fixed for iOS in the latest beta, which you can sign up for (free): https://beta.apple.com/sp/betaprogram/
Opening that pastebin hard-crashed firefox on my mac.
I’m running MacOS 10.12.5 and FireFox 58.0.2 and I was able to open the pastebin safely.
Are you running High Sierra or a different FF version?
I’m running MacOS 10.13.3 and FF 59.0b7.
Hmm. Opening that URL, or pasting the contents of the URL does not crash Safari or Terminal on my mac (10.12.6). cat-ing the file on my terminal also does nothing. I do notice that Safari does not render the glyph correctly (I probably need a Telegu - or is it Malyalam? - font) though terminal does. TextEdit renders correctly.