Narrow-linewidth lasers are in extensive demand for numerous cutting-edge applications. Such lasers operating at the visible range are of particular interest. Self-injection locking of a laser diode frequency to a high-Q whispering gallery mode is an effective and universal way to achieve superior laser performance. We demonstrate ultranarrow lasing with less than 10 Hz instantaneous linewidth for 20\documentclass[12pt]{minimal}
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				\begin{document}$$\mu$$\end{document}μs averaging time at 638 nm using a Fabry–Pérot laser diode locked to a crystalline MgF\documentclass[12pt]{minimal}
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				\begin{document}$$_2$$\end{document}2microresonator. The linewidth measured with a\documentclass[12pt]{minimal}
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				\begin{document}$$\beta$$\end{document}β-separation line technique that characterizes 10 ms stability is as low as 1.4 kHz. Output power exceeds 80 mW. Demonstrated results are among the best for visible-range lasers in terms of linewidth combined with solid output power. We additionally report the first demonstration of a gain-switched regime for such stabilized Fabry–Pérot laser diode showing a high-contrast visible frequency comb generation. Tunable linespacing from 10 MHz to 3.8 GHz is observed. We demonstrated that the beatnote between the lines has sub-Hz linewidth and experiences spectral purification in the self-injection locking regime. This result might be of special importance for spectroscopy in the visible range.