William Kilpatrick, 22, from Bannockburn, put the incitement to violence on the social networking site using his mobile, as he left the branch of Morrisons where he worked.
The post was made on the day of an Old Firm game in 2011 shortly after bombs and bullets had been sent to both Mr Lennon and Celtic supporter Paul McBride QC, who died last year.
It was reported to police by a supermarket colleague.
Dev Kapadia, prosecuting, said: "It was a misguided and reckless comment."
Kilpatrick claimed it was "just banter".
But after a trial at Stirling Sheriff Court lasting a day and a half, a jury of 10 men and five women found him guilty, by majority verdict, of causing a breach of the peace by posting a Facebook message that was of an offensive and threatening nature.
Sheriff Wyllie Robertson deferred sentence until October 23 for criminal justice background reports.