So it turns out you can fix the refresh rate if you disable resist fingerprinting. However, mull advises you not to do that, and not knowing much about it I learnt online the following details and now I prefer a lower refresh rate to disabling it -

"Resist Fingerprinting" is a privacy feature that can be found in various web browsers, including Mull Browser, which is a fork of Firefox focused on privacy. This feature aims to make users less identifiable and trackable across websites by minimizing the amount of information browsers reveal about users and their devices.

Web fingerprinting involves collecting details about a user's browser and device, such as screen resolution, operating system, installed fonts, and browser extensions, to create a unique identifier for tracking purposes. Each piece of information might seem benign on its own, but collectively, they can create a detailed profile that can uniquely identify a user, even in the absence of cookies or traditional tracking methods.

When "Resist Fingerprinting" is enabled, the browser attempts to reduce this uniqueness by:

• Providing websites with less detailed information or more generic information about the browser and the device.
• Limiting or altering the behavior of web APIs that can be used to gather unique information about the device or its user.
• Adjusting the content of HTTP headers to be less revealing or more uniform across users.

By doing so, Mull Browser and other browsers that offer this feature help protect users' privacy and make it more difficult for advertisers, analytics companies, and other third parties to track users across the web without their consent. However, it's important to note that while "Resist Fingerprinting" enhances privacy, it may also cause some websites to behave differently or break certain functionalities that rely on the information it restricts.