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I had a couple of .mht files which opened in IE, a browser I never use. I renamed their extension to .HTML to run it in Firefox. When I opened the file in Firefox, Firefox created new tabs endlessly. I had to close it to stop it.

Is this a security flaw in Firefox?

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Even if not a security flaw, it's a bug and submit it to FF's bugzilla – fatfredyy Jan 14 '13 at 7:39
It sounds like more of an annoyance rather than a security flaw. – Hammo Jan 14 '13 at 8:48
up vote 10 down vote accepted

Firefox does not support MHT files without addons.

It is possible that you have tricked Firefox into opening each MIME object from the MHT file into a new tab. It is doubtful that this could turn into a security flaw.


I confirm that behavior with a valid MHT file. It is a Firefox configuration issue. By default, Firefox will not recognize the MHT and will ask you for a "Open with" program. If you select to open with Firefox and check "Do this automatically for files like this from now on", then it goes into a loop and will open many new tabs. It will stop if you press the Escape key.

This Mozilla support article is about the same symptom and contains a configuration fix.

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