I don't know why -- and I don't know if it was legit. If it is, I hope somebody at the site can dispute the report.
But on Safeweb,
this site gets a Safe rating.
I tried to save the URL with the warning, but it didn't show anything. And it's one of those long URLs:
moz-extension://beeb3874-9e63-4966-8433-085de5a84786/content/ui/blockedPage.html?originalURL=https://www.mobileread.com/forums/&reportURL=https://safeweb.norton.com/report/show?url=https://www.mobileread.com/forums/&ulang=en&blockPageType=malicious&continueToSiteUR L=https://www.mobileread.com/forums/#