I have done localization changes outside of Zotero in text editor (and in another trunk version). NOT doing any localization changes in running Zotero or version installed. Just playing with menu options. It is definitely not connected with Zotero crash.

When clicking "Preferences" and menu "Proxies" is shown and freezes, first and second checkboxes are checked and .edu suffix is entered in other field. Well, I don't use any proxies and didn't entered that. After ca 10 seconds of freeze, Firefox crashes.

Not working: rebooting, restarting Firefox, deleting extension* files in Firefox profile directory.

1) in Firefox about:crashes there is no crash report or accident

2) Zotero real-time debug output from console (only last lines):

zotero(3): DATE: could not apply algorithms
zotero(3): DATE: retrieved with algorithms: ({year:2011, month:4, day:18})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:6, day:26})
zotero(3): DATE: retrieved with algorithms: ({year:2009, month:11, day:5})
zotero(3): DATE: retrieved with algorithms: ({year:2011, month:4, day:23})
zotero(3): Translate: WARNING: new Zotero.Translate() is deprecated; please don't use this if you don't have to
zotero(5): SELECT leafName, translatorJSON, code, lastModifiedTime FROM translatorCache
zotero(3): Cached 339 translators in 70 ms
zotero(3): Translate: Searching for translators for an undisclosed location
zotero(5): SELECT key AS domainPath, value AS format FROM settings WHERE setting='quickCopySite' ORDER BY domainPath COLLATE NOCASE
/usr/bin/firefox: line 142: 5877 Naruszenie ochrony pamięci $MOZ_PROGRAM "$@"

The last line is a Polish message: SEGMENTATION FAULT, and it is shown while crash after freeze.

openSUSE 11.1 (Linux 2.6.27.56-0.1-default i686, KDE 4.4.1). My Firefox is quite up to date (5.0, not 5.0.1, but the site you've linked is showing: 'Your Firefox is up to date') and I've get it from distro repositories (http://download.opensuse.org/repositories/mozilla/openSUSE_11.1/). I will try to reproduce this behavior in another fresh Firefox profile and let you know.

I am using the latest official stable Firefox release on Debian. I have the exact same issue. Zotero detected my use of a web proxy to access Google scholar, asked me if I wanted to use it thereafter (to which I agreed). Now the Zotero preferences window crashes. I have a separate profile for this version of Firefox so there's not some kind of cross-version issues.

I'd would post info from the debug console but I can't turn on the debug console (opening the preferences window crashes the browser).

Thanks. This is on Firefox 5.0.1 (bzip package downloaded from mozilla.org less than one week ago).

After opening the preferences window, here's what shows up in the debug log:

zotero(5): SELECT COUNT(*) FROM fulltextItems WHERE (indexedPages IS NOT NULL AND indexedPages=totalPages) OR (indexedChars IS NOT NULL AND indexedChars=totalChars)
zotero(5): SELECT COUNT(*) FROM fulltextItems WHERE (indexedPages IS NOT NULL AND indexedPages<totalPages) OR (indexedChars IS NOT NULL AND indexedChars<totalChars)
zotero(5): SELECT COUNT(*) FROM itemAttachments WHERE itemID NOT IN (SELECT itemID FROM fulltextItems WHERE indexedPages IS NOT NULL OR indexedChars IS NOT NULL)
zotero(5): SELECT COUNT(*) FROM fulltextWords
zotero(3): Cached 16 styles in 18 ms
zotero(3): DATE: retrieved with algorithms: ({year:2009, month:4, day:20})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:1, day:6})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:2, day:15})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:1, day:7})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:2, day:14})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:1, day:27})
zotero(3): DATE: retrieved with algorithms: ({year:2008, month:9, day:20})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:2, day:15})
zotero(3): DATE: retrieved with algorithms: ({year:2008, month:9, day:28})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:2, day:15})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:0, day:27})
zotero(3): DATE: retrieved with algorithms: ({year:2010, month:1, day:23})
zotero(3): DATE: retrieved with algorithms: ({year:2009, month:11, day:7})
zotero(3): DATE: retrieved with algorithms: ({year:2009, month:11, day:31})
zotero(3): DATE: retrieved with algorithms: ({year:2009, month:8, day:14})
zotero(3): Translate: WARNING: new Zotero.Translate() is deprecated; please don't use this if you don't have to
zotero(3): Translate: Searching for translators for an undisclosed location
zotero(5): SELECT key AS domainPath, value AS format FROM settings WHERE setting='quickCopySite' ORDER BY domainPath COLLATE NOCASE
Segmentation fault

Can one of you try the 2.1 branch XPI and let us know if it fixes the issue? If it doesn't, can you tell us what window manager you're running?