I am using Ubuntu 14.10 with dark theme , Today I have upgraded my firefox to developer edition (40.x)

previously i was on firefox 38.x

I use some of the sites where firefox default from.css styling doesn't fit well specifically text-area, input field and select boxes so in firefox 38 i have created chrome folder and placed userContent.css file inside that and it was working fine

but in this new developer version ( firefox 40.x) .. I did the same thing , Placed my CSS inside chrome folder of newly created profile but nothing is working

userContent.css file is not even loading ...checked in inspector path


below is the content of my userContent.css file

@-moz-document domain(elance.com) {
    textarea  {
        -moz-appearance: none !important;
        background-color: White !important;
        color: Black !important;

tried restarting firefox several times, no tweak seems to working

  • I am having this same problem on both of my Windows 10 machines and the other guy in my office who uses userContent.css is also having this issue on his Windows 8 machine. Very frustrating. We are also both using Developer Edition. – David Michael Gregg Jun 16 '15 at 4:28
  • still , i couldn't make it to work...tried everything..and everybody says userContent.css is only way to tweak your firefox's behavior.. (or change file in installation directory in user-agent css)...weird thing is it was working fine in previous versions ! – MrPandav Jun 16 '15 at 6:56

I identified a (disappointing) workaround which worked for both of my computers and my coworker. In Firefox Developer Edition...

  1. Go to Settings > General > Startup.
  2. Enable the option Allow Firefox Developer Edition and Firefox to run at the same time.
  3. Restart your browser.

Now, Firefox Developer Edition will still not recognize your userContent.css file—even if you reproduce that file in Firefox DE's own newly-independent profile folder. I still don't know why this is. I will suspect this is to be a bug until I hear otherwise. But now you can use the stable Firefox release alongside Firefox DE and it will recognize your userContent.css file.

In my case and that of my coworker's, we do not use Firefox DE on the same webpages for which we use userContent.css, so this workaround was acceptable. (This is likely true for most Firefox DE users, as it is, of course, for development purposes and why would a developer need to leverage userContent.css when he/she can use the Inspector or change the very source code itself?)

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On Firefox Developer Edition the userContent.css files don't appear to load properly if you have multi-process Firefox Developer Edition enabled (General -> Startup -> Enable multi-process Firefox Developer Edition). Once you disable this it appears to work.

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