Main Content

How To Tell Firefox to Open a DMG

If you are running Firefox on a Mac, you’ve more than likely came across the problem that it has no idea what to do with a .dmg file.

Ideally we’d want it to open the .dmg just like it does a .zip file and I’ve figured out how to do that.

Here is how to tell Firefox to mount a .dmg file on a Mac
1) Click here to go to Mozilla and click on the green Download Firefox button. This may sound odd, but it’s a must. This set of instructions will only work on this dmg for reasons that are probably hard to explain. Trust me here.
2) A window will pop up asking you what you want to do with this DMG. Click the ‘Choose…’ button.
3) Navigate to your-harddrive/system/library/CoreServices/ and choose DiskImageMounter
4) Click the ‘Do this automatically…’ check box to save the setting.
5) Hit OK. If you don’t actually want to download Firefox again, just cancel the download.

That’s it. All .dmg files should now open automatically.

If that doesn’t seem to work right, then go to Firefox -> Preferences -> Downloads and click on the ‘View & Edit Actions…’ button. Look for DMG, click on it, click ‘Change Action…’ and choose ‘Open them with this application’ and browse to DiskImageMounter again. This will clear up any confusion within Firefox but you must perform the steps above first or else you can’t even get DMG into the list.

To get Firefox to open .zip files with Apple’s BOMArchiveHelper instead of Stuffit go to Firefox -> Preferences -> Downloads and click on the ‘View & Edit Actions…’ button. Look for ZIP, click on it, click ‘Change Action…’ and choose ‘Open them with this application’ and browse to BOMArchiveHelper which is in the same CoreServices folder as DiskImageHelper.

27 Responses

  1. bousozoku says:

    Yes, of course, you can change Firefox to open and/or execute practically anything you might want to download. Is security not an issue for you?

    Even if current .dmg files aren’t a threat, what about the future?

  2. Thomas says:

    I was waiting for that. 🙂 Yes, automatically opening any file could be a security risk. But..
    1) I only download files from sites that I trust.
    2) Firefox works at stopping any site from automatically downloading files for me without my knowledge.
    3) I read many many Apple news sites and blogs so if there is a virus, I’d know.
    4) A dmg is like a zip or sit file. You are in control. If you tell the browser to automatically open it, then it’s your risk.

    So, no I’m not worried. If it’s an issue in the future, just go in to Firefox’s preferences and delete the setting.

    Don’t live in fear, just be educated.

  3. i want to open .dmg files

  4. Alan Fraser says:

    That did the trick. Thanks. I’ve been a long-time Safari hold-out but the last week has completely convinced me on Firefox. Regarding any security issue in opening the DMG, if you didn’t know the source then why would you download it in the first place.

    It’s odd that such an arcane process is required and I definitely appreciate your information on it. Thanks again.

  5. Paul says:

    Such a simple solution. I love it.

  6. brad says:

    How do i open DMG files on a win2000 machine ?
    found a site here, but i cant understand due to all the squabling !

    i got a program in a .dmg format.
    is this like a ZIP file ?

    thanks in advance,

  7. Thomas says:

    You’ll have to check out or some other Mac board for that kind of information. I’m not sure you can.

  8. Matt Heinrich says:

    Groovy, thanks.

  9. Mel says:

    This really helped. Thanks!

  10. julie says:


    suddenly my DISK IMAGE MOUNTER and DISK UTILITIES are GONE! and i cannot open any dmg files or zip files! i tried the firefox method but cannot find any disk utilities at all when doing an apple Find on my computer! and all the help i have gotten so far is to download some program, but they ARE ALL DMG s!!! HELP how can i get back to opening downloads so i can fix this?? i even tried opening my original Mac restore cd, but it wouldn’t / couldn’t read that either! what is going on! please help me !

  11. Thomas says:

    You need Apple support. It sounds like you deleted the program that reads DMGs and that’s not good. It has nothing to do with Firefox so this can’t help you. Go to Apples support forms and ask there.

  12. Boyce McJunkin says:

    tried your procedure for telling Firefox how to handle .dmg files. I can’t change anything in the preference panel for Firefox. When I download, it goes to another screen and sits there. Must have something wrong with
    my network settings because i can’t download in Safari either. IE works fine!

  13. Thomas says:

    You can’t get Safari to download DMGs? That’s some strict network.

  14. Dangr says:

    Hey, I tried your procedure, but didn’t get very far; I downloaded Firefox, but it didn’t ask me what to do with the file…. Any suggestions on other dmgs to download so that it would work?



  15. Thomas says:

    Dangr, is there any chance that .dmg is listed in ‘File Types’ in your Firefox’s preferences? Check it out and see if it’s already got a default behavior. If so, just update it.

  16. Luke says:

    Excellent solution.

  17. bill darst says:

    When I download ie., a printer dirver in the MacOSX format, instead of showing up as a dmg, it shows up as an exe file.
    If I download the same dmg file in Safari in will show up as a dmg file.

    Any fixes?


  18. Thomas says:

    That sounds like a website serving up a file based on what kind of machine it thinks you’re on. You haven’t change your user agent have you?

  19. JoeyShabadu says:

    In Firefox, the menus are somewhat different.

    Go to preferences and then click on CONTENT. From here, you can MANAGE your actions as previous.

  20. svedish says:

    I can’t seem to find the zip file type under “manage…” and there is no way to add a file type by hand (Firefox 2..x.x).

  21. Thomas says:

    svedish – Adding file types usually happens when you’re downloading a file. I agree Firefox should make it easier, but a Google search may come up with a better answer.

  22. mavo says:

    I figured out what the problem is and yes, it’s not intuitive at all. The problem is that there is no way to add a new file type by hand in the ‘manage…’ section of the Firefox File Types prefs pane. And the file types get added only when you download them yes, BUT (and this is the part that could drive somebody mad) the new file types get added to the list only when you tell Firefox to ‘Do this automatically for files like this from now on’ in the dialog box that appears when you try to download something.
    So, even if you don’t find in the dialog box the right action you want to assign for every file of that kind (e.g. open it with BOMArchiver, you’ll likely find only StiffIt Expander), you still have to choose something here, tell Firefox to do it every time, and THEN go into the prefs (again, Content>File Types>Manage…) where you have more control, and choose exactly how you want Firefox to deal with that kind of file.

  23. gus says:

    hey everyone. when I click on a link to download something in firefox & safari, It just goes to a blank screen and sits there, or loads and refreshes the previous page. I have to manually right click the link, and then save link as. but this doesn’t work for some files for example torrents on mininova. I would really appreciate it somebody could help me.


    PS i was using speed download a month or two ago…i then deleted it, attempting to get my firefox downloading for me again. I dunno if this made any difference to settings etc.

  24. Thomas says:

    Gus, it sounds like you need to ask the Speed Download folks how to fix that one.

  25. Demonike says:

    Hi there, I found your page by Google, searching for the same solutions you nicely provide here. Thank you.
    However, I’m also mad with the way FF handles ftp:// protocol. I’d want it to open the address in my FTP client (Transmit), not to give a listing in the browser window, where I cannot upload… I didn’t find that type of handler in the prefs although “mailto” was there. Since it is not a file, I cannot figure out how to configure this 🙁

    Any ideas?

    PS. Seems odd that such elementary things are so secretively tucked away somewhere…

  26. Murph says:

    Thanks man, worked great for me…

  27. NH says:

    Thanks much, worked like a charm!
    Funny that they only give you the ‘choose’ option when you’re downloading FF itself 🙂

Leave a Reply