[Firefox] Broken tab-indents in markdown code blocks #483

Tab-indented code in markdown is broken in firefox when refined-github extension is enabled:

This is how it should look (with disabled refined-github extension):

If I uncheck this line in the Firefox dev tools, the indentation is correct again: https://github.com/sindresorhus/refined-github/blob/68fd4d17f947089758f344b9f424286f3d39fe48/extension/content.css#L670

Space-indented code seems to work fine, though.