Whatever autocompletion plugin is used for the LibreOffice forums, is really hard to get ride of when submitting posts. It obscures the captcha UI.
Firefox, Windows 10.
Could you be more descriptive? Does it occur when tagging the question? When you enter something in the Search box?
Don’t use an answer to provide this additional information. Answers are reserved for solutions because this is no forum but a Question & Answers site. Edit your question.