I bet a lot of the extra error messages are due to the "cross-site XMLHttpRequest" feature. Bug 394390 also mentions security errors being repeated 3 times.
Summary: To many error msg for local file XHR reading directory listing → Too many error messages for local file XHR reading directory listing
Created attachment 280309 [details] no_line_number.png error console for "readother.html" (attachment 125538 [details]) also for DOM read there is no line number listed in ERROR MESSAGE
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