Ubuntu 20.04 LTS: can't start firefox

[mahesh]

Firefox is already running but not responding. To use Firefox, you must first stop the existing Firefox process, restart your device or use a different profile.

but
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$ ps aux | grep firefox
maketopsite         22126  0.0  0.0   8868   724 pts/7    S+   11:11   0:00 grep --color=auto firefox
$
Anyone know please what is wrong ?