The suspected Florida firebug accused of starting the blaze that turned into the devastating Palisades Fire was held without bail Thursday after a judge heard testimony that he threatened to burn his sister’s house down last month.

French-born Jonathan Rinderknecht, 29, was in an Orlando federal court Thursday — shackled and clad in red jail clothes — for a 90-minute hearing where ATF Special Agent in Charge Thomas Harrison told a judge about two September incidents in which an apparently unstable Rinderknecht was visited by the cops in Florida after making threats.

Prosecutor Rachel Lyons called Harrison to testify as she argued for Rinderknecht to be held in jail without bail on the grounds he’s a flight risk and a danger to the community.

Magistrate Judge Nathan Hill agreed to remand Rinderknecht until his trial. 

Earlier in the hearing, Harrison testified that during a Sept. 19 incident, Rinderknecht — who had been living with his sister and her husband for five months since leaving Southern California — threatened to burn his sibling’s Brevard County, Florida home down.

Then just six days later on Sept. 25, Rinderknecht’s father, who was visiting from France, reported to the cops he was concerned about his son having a gun.

A disturbed Rinderknecht said he might shoot his brother-in-law in self-defense but said the weapon was locked away in a safe. Investigators ended up finding the firearm hidden inside a teddy bear in the sister’s garage, the agent testified.

Rinderknecht’s sibling and her family moved out of the home and had been in the process of trying to evict an erratic Rinderknecht, Harrison testified.

Lyons said the fact that Rinderknecht has family in France and speaks the language makes him a flight risk.

She also said he could end up facing much harsher penalties than the five-to-20 years that come with a conviction on the charge he faces because of the aggravating circumstances. She said he might even face the death penalty.

Defense attorney Aziza Hawthorne argued he wasn’t a flight risk and noted that his family, including his brother and two sisters, were present in court to support him.

“He is not a risk to anyone,” Hawthorne claimed.

Rinderknecht, who is currently being held in Seminole County Jail is scheduled to return to Orlando court on Oct. 17 for an evidentiary hearing.

The Biden-supporting Uber driver is accused of “maliciously” starting the Palisades Fire on New Year’s Day, which — after burning for weeks — left 12 people dead, destroyed nearly 7,000 homes and businesses and caused about $150 billion in damages.

He made his initial appearance on Wednesday, where he acknowledged the hefty charges he’s facing.

Shackled at the ankles and wearing shorts and a T-shirt, he quietly told the judge that he was not under the influence and did not have mental issues, according to WKMG.

Rinderknecht, who officials said has no criminal history, faces charges including malicious destruction by means of fire.

Federal arson charges already carry steep mandatory minimum sentences that range from five to 20 years, but are even stricter if it leads to injury or death.

With Post wires