The 6-foot-high gate, stolen in November 2014, was found last December in a parking lot in Norway following an anonymous tip.
Increasingly, ideologues only call out anti-Semitism if it is carried out by their opponents.
An error indicating that the main Jerusalem-Tel Aviv highway was closed caused major traffic jams on the alternative route during the Wednesday morning rush hour.
The march in Sofia celebrating the Bulgarian alliance with Nazi Germany has been held annually since 2003.
The campaign by two Muslim activists has raised $66,000 in less than one day, far exceeding its $20,000 goal.