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[Exception... "The expression cannot be converted to return the specified type." code: "0" nsresult: "0x805b0034 (TypeError)" location: "<unknown>"]


everytime ,i see this warning, i can't use this add on

Hmm, never seen that and can't tell much at all from the error message. Can you let me know your OS, FF version (or if you're using Palemoon). Would you also please disable all other addons and then try FS again and see if it works? If it does, then enable other addons one by one and you'd find which addon is conflicting with FS.