For the last day or so, whenever I open zotero, firefrox completely freezes and I have to force quit firefox every time. All websites work and don't cause this problem.
That's likely just the auto-sync processing a large download. Give it a few minutes to finish. If you force-quit it, it will just freeze again the next time you open Zotero.
3.0b3, now available, shows a progress bar when syncing instead of freezing Firefox.
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3.0b3, now available, shows a progress bar when syncing instead of freezing Firefox.