I'm having trouble in signing up on Mozilla Account on Firefox browser. Whenever I try to sign up or sign in, this message shows "The request was blocked for security reasons".

Hey Shakib, It looks like you already have an account registered with us. You need to Log In, not Sign Up.

Would you help me signing up? I already created Mozilla Support account a while ago. But I'm still having that same problem.

The Account system that support.mozilla.org was using before has not been used since April 14, 2020 as you can only login with a Mozilla Account since. You are using a Mozilla Account to post this and your duplicate thread on this community support forum. Mozilla Account used to be called Firefox Account til November last year.

https://support.mozilla.org/en-US/kb/firefox-accounts-supportmozillaorg

This issue could be due to browser settings, network restrictions, or extensions. Try clearing cache, disabling VPN/ad blockers, or using a different network. I faced a similar problem creating an account to work for online store, and switching networks helped.