I have tried to search for this answer for quite some time and I have gone through all the various FAQ's and documentation regarding the three licenses; but none of them have been able to answer a question that I have.

So I've been working an idea for a website for sometime now and recently I found open source software that has many of components that are similar. It is licensed under the mpl/gpl/lgpl licenses. I think for the most part I understand the ramifications, due to the searches and reading, of what is required if I modify/use and want to distribute the software.

But what if I want to modify and not distribute, but use it on a public website that I generate ad revenue from? Is this illegal?

It doesn't seem like it is from reading other open source system, say like Drupal, where they allow you to use the software but it's not considered "distribution" if people just go to the website.

I know this site may not be the best resource and I've tried some other sites, but I haven't received any clear replies back. If you know some other resource that I could contact also, please let me know.

Links for those who don't know:

  • You might be well served to provide links to the licenses. I for one have never heard of "MPL". Commented Feb 11, 2011 at 17:25
  • 1
    @Crazy Eddie - the MPL is the Mozilla Public License and is fairly well known in OSS circles. Commented Feb 11, 2011 at 17:29

2 Answers 2


IANAL - For the GPL/LGPL, at least, the license is triggered upon distribution, so you are not required to do anything if you're using it on the server side of a website. Common courtesy, of course, would say if you make any bug fixes, etc., that you should contribute that back to the community. In fact, it would be nice of you to redistribute it just to be nice (I understand how this could be impossible if you mix non-GPL compatible code with GPL code though).

Note that this is why the AGPL was created. If you find something that's AGPL, you can't use to run a public website without releasing any changes.

  • Thanks for the fast reply. I'm going to do some more research and I still have whether or not it will work.
    – tomok
    Commented Feb 12, 2011 at 4:15

According to http://www.gnu.org/licenses/license-list.html the MPL is on the list of licenses which are not GPL compatible. Therefore a combined work which derives from both MPL and GPL code cannot be redistributed at all unless you can get special permission from the authors to relicense it in some compatible way.

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    Yes, I think I something similar on the Mozilla license page.
    – tomok
    Commented Feb 12, 2011 at 4:16
  • That is true for some versions but not all. GPL3 is compatible with MPL2 according to your link. Commented Mar 27, 2016 at 8:41
  • @EsbenSkovPedersen The MPL 2.0 was released January 3, 2012. Nearly a year after my answer. So I was a bad prophet. But my answer remains true for 1.x versions of the MPL, and was true for whatever software the questioner was interested in back in 2011.
    – btilly
    Commented Mar 29, 2016 at 21:25

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