Thanks for the feedback. I've created the following issue to address the font size: https://github.com/Kobee1203/source-viewer-web-extension/issues/15
As for the flickering, it’s difficult to further optimize this behavior when using the context menu (“View Page Source”), because the extension overrides the native function and has to perform a few checks before displaying the viewer. The issue isn’t visible when you click directly on the extension icon because there’s no function substitution, it opens directly in the extension. Anyway, I’ll see if I can optimize that 😊.

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You can test the new release 1.9.0, I added a new feature to adjust the font size. Hope you like it 😊.