Hi, Avast Prob saw it as a False/Positive. Where did you download it from a mozilla.org or firefox.com all other except a few are bogus and it could very well be. If not downloaded from a official site run some scans :

• https://www.malwarebytes.com/
• https://www.adlice.com/download/roguekiller/ portable

Note if get errors opening pages it will be Avast and you will need to go to their forum for a work around. Especially the below message :

• https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

Please let us know if this solved your issue or if need further assistance.

i download it from https://www.mozilla.org/en-US/

mtech.netcafe said

i download it from https://www.mozilla.org/en-US/

It is good. So just a false/positive I would say.

It is never a problem to run those 2 programs as they look for things differently than a regular A/V program does.

what's the exact detection info (filename/threat name) that avast is giving?

Note that some AV software sees the small Firefox stub installer as containing a virus. The solution is usually to download and save the full Firefox installer.

• https://www.mozilla.org/en-US/firefox/all/