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To determine which extension it is, you should open your browser in normal mode (not incognito or 'browse in private' mode) and disable all the extensions. Then re-enable each extension one-at-time, returning to Blackboard Collaborate Ultra each time to check if the issue has returned. This process narrows down which extension is causing the problem.
How you manage your extensions differs from browser to browser, but here are instructions for accessing your extensions in the most commonly used browsers:
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