Are you sure that's the only thing that changed? From your screenshot it looks like you're using a very low screen resolution (800x600?). Unless you're on a very old netbook, that shouldn't be the case. Maybe there's something wrong with your graphics driver?
You can try resizing the three Zotero panes by dragging the separators in between them, but the full Zotero pane doesn't really work at resolutions that low, and hasn't in years. (Presumably missing half the right-hand pane of Zotero is a larger issue here than the sync icon.)
I had the same issue when I migrated to a new office computer that was set to 800x600 resolution. I rediscovered the sync button by pulling the separators to the left and then changed screen resolution.
Upgrade Storage
http://www.zotero.org/support/reporting_bugs#provide_steps_to_reproduce
It may help to take a screenshot, upload it somewhere (e.g., imageshack.us), and provide a link here.
You'll notice at the far right edge of the zotero toolbar, just past the green arrow, there is no sync button.
Thanks.
You can try resizing the three Zotero panes by dragging the separators in between them, but the full Zotero pane doesn't really work at resolutions that low, and hasn't in years. (Presumably missing half the right-hand pane of Zotero is a larger issue here than the sync icon.)
I had the same issue when I migrated to a new office computer that was set to 800x600 resolution. I rediscovered the sync button by pulling the separators to the left and then changed screen resolution.