maybe the same issue as here: https://support.mozilla.org/en-US/questions/971876?

Looks like the same problem indeed. And like my case...this is a new thing..it is driving me crazy!

could you tie the change to the last firefox update?

maybe it's a bit far fetched, but you could try to enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named browser.download.manager.scanWhenDone. double-click it and change its value to false.

http://kb.mozillazine.org/Browser.download.manager.scanWhenDone

Thanks a lot philipp, I just tried it but still no joy. I am certain this did not start with the latest update. FF 24 was respecting group permissions up untill 2 days ago!

can you try to replicate this behaviour when you launch firefox in safe mode once and download a file?

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

here's another question from yesterday which connects that behaviour to the update from 23 to 24: https://support.mozilla.org/en-US/questions/975473

Trying the safe mode was one of my very first attempts, I assumed it could be an extension or a plug-in causing this but no use. Now I have to manually change every file's permissions after downloading it or open Safari each time I download anything. Still pretty sure FF 24 worked fine before, but I could be wrong. Maybe I should try a downgrade?

though downgrading is normally not recommended, you could just use it to test if it has really been caused during the update from 23 to 24: Install an older version of Firefox

i'm still trying to find out if this has been a deliberate change (maybe to address some security concerns) - otherwise it's probably best to file a bug for that issue...

I'll certainly try the downgrade this problem is a real nuisance. I can understand it might be for security, but when downloading a file into a shared folder it means you intend to access it all over the network.

Thanks a lot for your help philipp

Happy to report this very annoying problem is now gone. I just updated to FF 25 and now downloaded file permissions are back to normal, with group access allowed.

I'm having this problem too. Using Firefox 26 and Mavericks. Tried the about:config change but doesn't fix it.

It was fixed in FF 25...Are you sure it is back in FF 26 ??!!

Yes, looks like it's back unfortunately.

Tried to switch to Firefox Extended Support Release 24.2.0 which fixed the issue. Discovered a discussion about the fact that the bug is back in v. 26 here: https://bugzilla.mozilla.org/show_bug.cgi?id=919076

Can't thank you enough for the heads up!

I guess I will never upgrade from FF 25 then. That seemingly benign bug causes massive headaches if you intend to access files from different nodes in the same network. Caused my Western Digital Live to stop having permissions for .srt files downloaded to my IMac.