That's possibly related to https://bugzilla.mozilla.org/show_bug.cgi?id=1233434 (Linux: temporary download directory is not created specifically for each user).
** Bug watch added: Mozilla Bugzilla #1233434 https://bugzilla.mozilla.org/show_bug.cgi?id=1233434 -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to firefox in Ubuntu. https://bugs.launchpad.net/bugs/1527884 Title: Firefox 43.0: Downloads fail Status in firefox package in Ubuntu: Confirmed Bug description: My firefox just got updated to 43.0. Starting with the update, all downloads fail. There is no file selection dialogue any more, just the blue arrow appears - and the downloads list says "Failed". I have tried the same on a clean profile with no add-ons, and downloads still fail. In the browser console, I get the following error message on each download attempt: [Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIAnnotationService.setPageAnnotation]" nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)" location: "JS frame :: resource://app/modules/DownloadsCommon.jsm :: onDownloadChanged :: line 735" data: no] Steps to reproduce: Klick on any downloadable file on a website (e.g. ZIP oder PDF). Result: Blue arrow appears, downloads list says "failed" below the download filename. The file will not download. Expected result: File dialogue (with appropriate settings). File being downloaded from the internet. Versions: Kubuntu 14.04.3 LTS Firefox 43.0+build1-0ubuntu0.14.04.1 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1527884/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp