Im using a js script on my website which only crashes in Firefox,
- User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.96 Safari/537.36
Sorry, but this forum is for end user Firefox support not for web developer issues. Please see this - Where to go for developer support
Mozilla web development StackOverflow thread. https://stackoverflow.com/questions/tagged/firefox+or+firefox-os+or+html5-apps
Or you could try posting at the Web Development / Standards Evangelism forum over at the MozillaZine fora. The contributors over there are more knowledgeable about web page development issues with Firefox. http://forums.mozillazine.org/viewforum.php?f=25 You'll need to register and login to be able to post in that forum.