Coroner Andrew Walker said online material viewed by the 14-year-old on sites such as Instagram and Pinterest “was not safe” and “shouldn’t have been available for a child to see”.
Molly’s father Ian Russell subsequently asked Meta chief Mark Zuckerberg to “just listen … and then do something about it”.
Welling up as he concluded a press conference in Barnet on Friday, Mr Russell’s voice broke as he said: “Thank you, Molly, for being my daughter. Thank you.”
Concluding it would not be “safe” to rule Molly’s cause of death as suicide, Mr Walker said the teenager “died from an act of self-harm while suffering depression and the negative effects of online content”.
At North London Coroner’s Court, he said: “At the time that these sites were viewed by Molly, some of these sites were not safe as they allowed access to adult content that should not have been available for a 14-year-old child to see.
“The way that the platforms operated meant that Molly had access to images, video clips and text concerning or concerned with self-harm, suicide or that were otherwise negative or depressing in nature.
“The platform operated in such a way using algorithms as to result, in some circumstances, of binge periods of images, video clips and text – some of which were selected and provided without Molly requesting them.
“These binge periods, if involving this content, are likely to have had a negative effect on Molly.”
The inquest was told Molly accessed material from the “ghetto of the online world” before her death in November 2017, with her family arguing sites such as Pinterest and Instagram recommended accounts or posts that “promoted” suicide and self-harm.
Meta executive Elizabeth Lagone said she believed posts seen by Molly, which her family say “encouraged” suicide, were safe.
Pinterest’s Judson Hoffman told the inquest the site was “not safe” when Molly used it.
Shadow digital, culture, media and sport secretary Lucy Powell said it was a “scandal that just as the coroner is announcing that harmful social media content contributed to Molly Russell’s death, the Government is looking to water down the Online Safety Bill”.
Online safety campaigners at the children’s charity NSPCC said Molly died after suffering from “negative effects of online content” and it should “send shockwaves through Silicon Valley”.
Out of 16,300 posts Molly saved, shared or liked on Instagram in the six months before her death, 2,100 were related to depression, self-harm or suicide, the inquest was told.
The court was played 17 clips the teenager viewed on the site – prompting “the greatest of warning” from the coroner.
The inquest also heard details of emails sent to Molly by Pinterest, with headings such as “10 depression pins you might like” and “new ideas for you in depression”.
Continuing his conclusions, Mr Walker said: “Other content sought to isolate and discourage discussion with those who may have been able to help.
“Molly turned to celebrities for help, not realising there was little prospect of a reply.”
A spokeswoman for Meta said in a statement following the conclusion that the company is “committed to ensuring that Instagram is a positive experience for everyone, particularly teenagers” and would “carefully consider the coroner’s full report when he provides it”.