Does the error happen in a Private Browsing window? Maybe Firefox cached some "site not found" result it shouldn't have? This sounds more like a server configuration issue than a Firefox bug.
__Edit: I installed the lastest Firefox v67, the problem is gone. It works great.__
Thanks. no it's not in a private browsing window.
I also asked other people to visit the site(mydomainname.com) from their computers and phones, all worked fine.
The hour long struggle left me with painful memories. :) I never had issue like this previously in Firefox or other browsers. On that day, Chrome and IE worked without problem on my computer (Win 7 32bit), so the computer should not be the culprit.
That leaves Firefox v66 standing. I don't know why.
Thanks. no it's not in a private browsing window.
I also asked other people to visit the site(mydomainname.com) from their computers and phones, all worked fine.
The hour long struggle left me with painful memories. :) I never had issue like this previously in Firefox or other browsers. On that day, Chrome and IE worked without problem on my computer (Win 7 32bit), so the computer should not be the culprit.
That leaves Firefox v66 standing. I don't know why.