I'm unclear what you're asking -- as per this thread (and confirmed by John's repeated laments above), saving from JSTOR via Safari when going through a proxy is (pretty much) broken at this time, even with the Safari Extension. We'll post here when there's a fix.
If you have problems with the Zotero Safari Extension beyond JSTOR, please start a new thread.
(that said -- you shouldn't be using Firefox 35 in any circumstances. Either use the current extended support version (31.7 or .8, I forgot) or, more typically, the current regular version (38). Using outdated Firefox versions exposes you to security risks and may also mean that you're subject to Firefox bugs since fixed.
I believe the Safari/JSTOR issue is finally fixed. Update translators from the general tab of the Zotero preferences, restart Zotero Standalone and Safari and try again.
Sorry for the long time this took--the actual fix was only possible because JSTOR changed the site, otherwise this was still a good bit out.
Upgrade Storage
If you have problems with the Zotero Safari Extension beyond JSTOR, please start a new thread.
Sorry for the long time this took--the actual fix was only possible because JSTOR changed the site, otherwise this was still a good bit out.
And so endeth the repeated lamentation.