Thanks Cameron for the tip! All the CSS for the packaged version of Fava gets compiled into a one big app.css, but I was able to find the relevant class and adjust it.
I'm a developer myself... but let's say that CSS and I aren't very good friends, so your pointer was very welcome :)
Anyway, I feel like this is sort of a bug then. Mi local currency has been losing value by the minute for years now, but Argentinian politics aside, there are other currencies were large figures are common (like the Chilean peso, from the top of my head).
Maybe it also depends on the monitor DPI, the browser, and other conditions, but I feel like this should be more dynamic, somehow. I have no idea how though.
I'm still curious as to why this doesn't come up more frequently, but maybe it's just that we users outside USA/Canada/EU are a tiny minority.
For now I'll keep setting the width to my linking whenever Fava gets updated.
Thanks!