My problem started when FF was repeatedly trying to automatically upgrade to 35.0.1. It repeatedly failed the incremental upgrade and said I should download from Mozilla.org. However, after doing that and installing 35.0.1 both addons and application support for links were broken and did not work. I have tried various solutions including deleting mimeTypes.rdf, deleting FireFox and all associated settings using AppZapper. A clean install of FireFox still is having the problem. When I try to add any addon, such as AdBlock, I see the message "There was an error downloading" as in the attached image. https://support.cdn.mozilla.net/media/uploads/images/2015-02-07-07-12-42-8eb8ad.png Similarly if I click on any link which would download a file, it always fails as in the following image where I attempted to download FireFox. https://support.cdn.mozilla.net/media/uploads/images/2015-02-07-07-19-04-eb8857.png However, if I click on the download retry widget next to the failed download it will succeed as in the attached image. These issues first arose after FireFox could not upgrade itself and I did a manual download and install of 35.0.1. Initially, I could not cleanly quit FireFox. It always aborted when I selected Quit. However, since my AppZap delete and reinstall it does quit cleanly. Although, I can not seem to get Addons and link support to work. With out Adblock I really can not use FireFox. I also use Chrome and Safari. Those are behaving normally. I also used Disk Utility to repair permissions. Nothing was listed in any directory associated with FireFox. Any suggestions as to how to correct?