I'm wondering about privacy aspects of Safari extensions, or which pieces of information active extensions can obtain about my web browsing activities. Should I expect that an extension will generally be able to collect information about everything I'm doing in Safari, or are there any restrictions on what extensions can access? The question is it possible to disable Safari extensions when using Private browsing? seems to indicate that there may be privacy issues when extensions are enabled.
More specifically, I'm interested in the Google Scholar extension that installs a button in the toolbar. Should I expect that this extension communicates information to Google only when I'm actually clicking the button, or can it communicate more?