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Previously, the UNMHT extension was used for this purpose. But since WebExtensions became the only option, UNMHT is not available. How to open these files on Firefox?

ARX
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2 Answers2

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To display MHT files:

  • Use IE or Chrome, since they both support the filetype natively, or
  • Use an outdated version of FF that still supports the UnMHT extension.

To migrate MHT files (e.g., to be displayed in modern FF):

  • After displaying the MHT file in a browser, re-save the page as "Web Page, Complete", and optionally serve converted MHT files over localhost with a web sever (e.g., Python 2's SimpleHTTPServer) to FF so Save Page WE can access and convert them, or
  • Use MAF on an outdated version of FF to bulk convert MHT files into another format.

Needless to say, outdated versions of web browsers are unsupported and have known unpatched security vulnerabilities. For instance, Firefox 58 is forever vulnerable to the Pwn2Own exploit that was publically demonstrated back in March 2018.

Additionally, Mozilla will be deleting legacy add-ons that rely on XUL/XPCOM technologies from AMO, so the downloads for MAF and UnMHT will disappear from that site in the future.

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Exactly one year later, it looks like Chrome does not support MHT files anymore but Windows offered me the option to open it in... Word 2016. It worked and I am able to save it as a PDF file that is more portable :-)

Same outcome for Chrome as for Firefox... Maybe due to similar integration of WebExtensions and/or discard of ActiveX support . But it still works in IE 11 ;-)

Google Chrome version 77 does not support MHT files. V

Pierre de Grenoble
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    It's still supported. You have to enable it from: chrome://flags > Save page as HTML – dns Dec 18 '19 at 16:19
  • @dns, many thanks for the tip. Although I can't see this flag under Iron version 77, a Chromium app without all the Google Chrome spying stuff, I was able to open any MHT page in Iron. May this feature have been fully implemented over time? One more thing: is there a way to save whole web pages as single MHT files under Chrome? As I definitively prefer to have a single MHT file than a association of a file and a folder made of an HTML main page and a folder containing all the files related to the web additional resources. – Pierre de Grenoble Dec 23 '19 at 09:39
  • You have to type **chrome://flags** on address bar, and then type on **"Search flags"** box, type: **MHTML**. Set to **Enabled**. This feature is already implemented for ages. – dns Dec 24 '19 at 19:27
  • I did this but not flag related to MHTML is listed. Reading MHTML single whole files is natively implemented in version 77 of Iron but there is no native option in the contextual menu of a page to save it as a single file. I found several extensions for Iron (Chromium) and Firefox to do that and I chose the same one called SingleFile for both browsers. It works like a charm and it has a lot of options to tune the way pages are saved and it is accessible from the context menu, the main menu or a button from the toolbar – Pierre de Grenoble Dec 25 '19 at 21:17
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    Try Google Chrome instead Chromium. Many things are removed from Chromium. – dns Dec 25 '19 at 23:48
  • @dns, thanks for the advice but as an European citizen, I am too concerned by the violation of my privacy by GAFA(M), especially Google. So I don't use Google any services and products except Youtube without any Google account. Instead I installed the new version of the Microsoft Edge which has switched to the Blink engine in January and it works like a charm. It natively integrates the option to save MHTML pages too. I will stick on that browser and Iron for managing MHTML pzhrd along with Firefox which is my default browser for a daily use. – Pierre de Grenoble Mar 08 '20 at 10:33