How do i run a Sikuli command in a Xvfb headless running firefox and selenium test case

Command i executed ,NOTE: DISAPLY is the port in which xvfb is running.
Executing command: export DISPLAY=:4015 ; echo 'welcome' |sudo -S java -jar -Djava.awt.headless=false -Dsikuli.Debug=3 /home/fnmst001/sikuli/Sikuli.jar doubleClickAction /home/fnmst001/sikuli/headlessZipFile.png

Output: (0,Argument length: 2
Executing doubleClickAction
[debug] Debug.init: from sikuli.Debug: on: 3
[debug] RunTimeINIT: lsb_release -i -r -s
[debug] RunTimeINIT: loadOptions: check: /home/fnmst001
[debug] RunTimeINIT: loadOptions: check: /root
[debug] RunTimeINIT: loadOptions: check: /root/.Sikulix/SikulixStore
[debug] RunTimeINIT: global init: entering as: API
[debug] RunTimeINIT: ScreenDevice 0 has (0,0) --- will be primary Screen(0)
[debug] RunTimeINIT: Monitor 0: (0, 0) 1920 x 1080
[debug] RunTimeINIT: runs as Sikuli.jar in: /home/fnmst001/sikuli
[debug] RunTimeINIT: exists libs folder at: /root/.Sikulix/SikulixLibs_201510081336
***** show environment for API (build 201510081336)
user.home: /root
user.dir (work dir): /home/fnmst001
user.name: root
java.io.tmpdir: /tmp
running 64Bit on Linux (0 Ubuntu 18.04) from a jar
java 8-64 version 1.8.0_222-8u222-b10-1ubuntu1~18.04.1-b10 vm 25.222-b10 class 52.0 arch amd64
app data folder: /root/.Sikulix
libs folder: /root/.Sikulix/SikulixLibs_201510081336
executing jar: /home/fnmst001/sikuli/Sikuli.jar
*** classpath dump sikulix
*** classpath dump end
***** show environment end
[debug] RunTimeAPI: global init: leaving
[debug] RunTimeAPI: initAPI: entering
[debug] RunTimeAPI: initAPI: leaving
[debug] RunTimeAPI: loadLib: libVisionProxy.so
[debug] Mouse: init
[debug] KeyBoard: init
2019-12-04 09:27:09 INFO Sikuli:18 - Number of Screens: 1
2019-12-04 09:27:09 INFO Sikuli:19 - Primary Screen: S(0)[0,0 1920x1080] E:Y, T:3.0
2019-12-04 09:27:09 INFO Sikuli:25 - Using Primary screen
2019-12-04 09:27:10 INFO Sikuli:28 - Screen capture: /home/fnmst001/sikuliximage-1575451629842.png
[debug] Image: loaded: /home/fnmst001/sikuli/headlessZipFile.png (file:/home/fnmst001/sikuli/headlessZipFile.png)
[debug] Image: cached: /home/fnmst001/sikuli/headlessZipFile.png (1 KB) (# 1 KB 1 -- 0 % of 64 MB)
[debug] Region: find: waiting 3.0 secs for P(/home/fnmst001/sikuli/headlessZipFile.png) S: 0.7 to appear in S(0)[0,0 1920x1080]
[debug] Region: find: P(/home/fnmst001/sikuli/headlessZipFile.png) S: 0.7 has not appeared [1532 msec]
2019-12-04 09:27:14 ERROR Sikuli:55 - FindFailed: can not find P(/home/fnmst001/sikuli/headlessZipFile.png) S: 0.7 in S(0)[0,0 1920x1080]
  Line 2189, in file Region.java

[debug] RunTimeAPI: final cleanup
[debug] FileManager: deleteFileOrFolder:
/tmp/Sikulix_2001260413
[sudo] password for fnmst001: )

i see a black screen in place of a file Explorer in sikuli snapshot, though the browser is visible.

Please help, Thanks in advance!