remember mismatched domains

I’ve whined about this before. Each time I use the web interface to acess my email account Firefox presents a Security Error: Domain Name Mismatch warning. The warning occurs because the secure URL I connect to is within my domain while the security certificate is issued to Dreamhost, my hosting provider.

Now, technically Firefox is entirely correct in advising me of the issue. What irks me is that I have no way of storing the fact that I am aware of the mismatch and no longer need my browser to bring it to my attention each time I check my mail. Obviously the ideal way to avoid the warning is to correct the problem that is being identified – obtain a SSL certificate for my webmail domain. Realistically though the expense involved does not make it practical. So, after searching for a quick fix and reading through some mildly entertaining flame wars I did what one does in this day and age of the extensible web browser: I built a Firefox extension.

The Remember Mismatched Domains extension for Firefox adds a “Don’t warn me about this certificate for this domain again’ checkbox to the Domain Mismatch warning window. When selected the domain name and security certificate domain pair is stored in a Firefox preference and the security error dialogue will be bypassed on subsequent visits.

Before trying out this extension I would recommend you read the discussion of a similar entry in the Thunderbird bugzilla database:
In particular this entry from Nelson Bolyard struck me as particularly insightful.

Security Error: Domain Name Mismatch

The 0.1 beta version of Remember Mismatched Domains can be installed from here:

It’s a beta and could use some testing in different environments. The comments section would be a good place to let me know of any issues or drop me an email.

update: just uploaded version 0.4. Details on the changes here.

update: Now at version 0.5. Which adds support for Thunderbird. Details here.

17 Responses

  1. Tomas Vilda says:

    September 11, 2005 at 8:14 am

    Hello, I would like to ask you how could I make my extension to disable domainMismatch dialog to appear. My extension goes to specific page and display stats, but I get that domainMismatch dialog. Could you suggest how to disable this thing in my extension?

  2. andrew says:

    September 11, 2005 at 7:00 pm


    Well the way the rmd extension manages it is by overlaying the DomainMismatch window. Basically, it then accepts the certificate in the window’s onload event. You could probably take a similar approach…

    Grab the extension and take a peek if you like. Feel free to re-use anything in it that’ll help. Let me know if you need more details.

    Course another approach might be to run both extensions.


  3. Ned says:

    October 26, 2005 at 9:55 am

    thx for the fix! :) Made my day.

  4. Laurens Holst says:

    February 1, 2006 at 9:55 pm

    Very useful! You should get it listed on!

  5. Ben says:

    February 28, 2006 at 8:15 pm

    DUDE I LOVE YOUR EXTENSION…. wow that can sound wrong!

    You have saved me so much time. Thank you!

  6. andrew says:

    February 28, 2006 at 10:25 pm


    Glad ya find it useful Ben.

  7. rahul says:

    March 17, 2006 at 6:52 am


  8. john says:

    March 12, 2007 at 11:35 am

    any chance of making this extension work for regular mozilla mail (when I try to install it, I get a “Install script not found” error).


  9. Andrew says:

    April 3, 2007 at 4:55 am

    Any chance of an update for Firefox 2? This looks like a great extension.

  10. andrew says:

    April 3, 2007 at 9:21 am

    Hey Andrew,

    The current version of RMD is 1.4.1 and it supports Firefox 2 (Windows and Linux). You can always find the latest version from here:


  11. Stephen says:

    April 21, 2007 at 11:32 pm

    I love this extension, we use it at work all the time!! (I work for a web-host, and its a common issue with Shared servers).

    Anyway, there is a bug with it in Thunderbird 2. It prevents me from sending any emails via a SSL SMTP port, 465 (if memory serves). I disable the extension and I can send emails with no issues.

    Any thoughts?

  12. Matej says:

    April 24, 2007 at 5:22 am

    You sir are a GENIUS!
    Great extension!

  13. Lennart Weijl says:

    April 16, 2008 at 7:01 pm

    You truly made my evening here!!
    Got the same problem you discribed, and this fixes it nicely!

    Works great, even on OSX!

  14. Denali Lumma says:

    April 28, 2008 at 7:42 pm

    This is great. I wish there was something like this for internet explorer, as well.

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    Pretty sure he will have a good read. Thanks for sharing!

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