I’m working on improving the performance of the browser add-on or, more specifically, the server that powers all checks run by the add-on. Performance is good during times of low load, but becomes bad when the server is under load:
One reason seems to be spell checking. Creating suggestions for unknown words is one of the main factors that make the server slow. Because of that, I have now limited the number of suggestions for German and French (which use hunspell, which is especially slow): only the first up to 30 unknown words will come with suggestions. If there are more unknown words, they will be detected as unknown but there will not be a suggestion for the word. We’ll see whether that helps.