Vast majority of webpages shouldn’t break, I’m saying that as a web programmer. I myself override fonts on a couple sites that I use regularly (namely Wikipedia). Where it might go wrong is in edge cases, e.g. small special snippets of text like captions for images, which can be designed to fit in limited space and use condensed fonts.

Not sure that browsers allow overriding all fonts on webpages (ever since sites specify specific fonts instead of just ‘serif’ and ‘sans-serif’), but there are likely extensions that can do that dynamically and forcefully. I do that via CSS in the Stylus extension, but that’s specific to particular sites and can’t work everywhere.

Basic website design is supposed to allow the user to set their own fonts and font sizes along with formatting based on screen size and orientation. Yes, a lot of pages are designed terribly and might break, but that is because they made a shitty website and not because you chose to use the internet the way it is supposed to work.

Changing out for a font that looks very similar to Ariel but with easier to differentiate capital I and lower case l should work fine.

You can set a specific font in your browser settings and force it to use that font on websites.

Most websites should at least support specifying a generic “serif” preference and then they pick a specific one, however you should also be able to force a local font via either browser options or extension