I read online before that J.Jonah Jameson's wife was murdered by a man in a mask, so he hates anyone in a mask, which sounds a bit odd, is that supported in canon?
Do we know exactly why he hates Spider-Man so much?
Jonah has accomplished many things in his life. He was an award winning reporter and was active during the Civil Rights Movements. He did a series of stories on the KKK, exposing members, meeting places, and generally doing whatever he could to drag them into the public and humiliate them/lead to some arrests. He's actually been chased down and threatened with death by them. Ever since then, Jonah's mistrusted anyone in a mask, especially people who take the law into their own hands the way he feels Spider-Man does.
Jonah's son John Jameson was an astronaut who was never afforded the fame Jonah felt his son deserved, while Spider-Man, a vigilante is lauded all over New York. John would also become known as the Man-Wolf at a later time in his life.
Secretly, we learned that Jonah has more than a little jealousy of Spider-man's power and influence in society.
From Amazing Spider-Man #10
Most modern readers don't know the depth of Jameson's hatred of Spider-man. For a time Jameson hired or paid someone to create super-powered villains to attack Spider-Man
The Scorpion was one of the first villains financed by J. Jonah Jameson to destroy Spider-Man.
- Former private investigator Mac Gargan was hired by J. Jonah Jameson to find out how Peter Parker was able to get incredible pictures of Spider-Man.1 Gargan's efforts to locate Peter in order to find out the truth triggered Parker's spider sense, making him easily avoidable every time.
The Scorpion, then and now; still as dangerous as ever.
- Frustrated, Jameson decided to pay $10,000 to Gargan to be the subject of an experiment. The experiment, created by Dr. Farley Stillwell, a researcher in animal mutation, which endowed the subject with the characteristic of another animal. Unfortunately the process resulted in the loss of Gargan's sanity, and the creation of the super-powered criminal menace known as the Scorpion.[Amazing Spider-Man #20]
He would later decide he wanted to take his revenge personally and hired mad scientists to create robots called Spider-slayers to kill the Wall-Crawler.
The first series of Spider-Slayer robots were originally designed and built by Dr. Spencer Smythe with the financial backing of J. Jonah Jameson who piloted them for the pleasure of personally hunting the superhero he hated for capture.
Spencer Smythe along with several Spider-Slayers
In Amazing Spider-Man #603, Jameson (now Mayor of New York) has some old Spider-Slayers sent to him from storage, to better equip his "Anti-Spider Squad" to take down Spider-Man. The Spider-Slayer technology is combined with that of the Mandroid suits. However, the "Spider-Slayer Squad" wearing the suits quit their jobs after Spider-Man saves them and New York from a dirty bomb.
Curiously enough, one episode of the early-mid 90's animated spider-man series, "The Sting of the Scorpion," went into more detail on this- in a flashback a masked mob enforcer tried to intimidate a younger J. Jonah out of printing a story; when Jameson ran it anyway said enforcer took a shot at him but missed, killing Jameson's fiance instead- Jameson just lumped Spider-man with other people "who wear masks and think they're above the law".