I was using the newest version of Pale Moon on a fairly clean install of Windows 7 on my decade-old-laptop. For some reason, Pale Moon can’t load the page, while Supermium browser can. (both of these are about 10 versions behind major browsers). I tried to change my useragent for the forums to ChromeOS 126; but no luck, still.
Some of the lesser known browser (Like pale moon, never heard of it before) don’t offer all the tools, and don’t support all the modern HTML tags, CSS rules, and other browser technologies required by modern sites.
You can just use another browser here on the forum, (or if you really want to) contact the forums development team, Discourse.
A mainstream browser that someone may had never heard of, nice nice.
While I certainly have heard of and used this browser before, I used it for some legacy stuffs. So I strongly doubt whether Discourse is willing to devote time into supporting older browsers like this one. Their browser support chart is always radical anyways.
If the Discourse devs are as sensible as I think they are, they are not such idiots to do browser support by checking user agents. The right way to do it is to do feature detection on the features themselves.
Supermium seems to follow the Chromium project quite closely, whereas Pale Moon seem to have been forked for Firefox much longer ago. Supermium also seems to at least try to stay close to Google Chrome, whereas Pale Moon really want to build something different.
Given that Pale Moon is a much smaller project, and with how complex browsers are nowadays, I think the Pale Moon developers will have a very hard time keeping up with all the development of modern browsers. I suspect that you’ll run into more compatibility issues by sticking to it.
If I may offer some unprompted advice: Windows 7 has not received any updates in over 4 years, and probably contains many security issues that will not be fixed. If your laptop cannot run Windows 10, I would personally go for a lightweight Linux distribution. At least that way you can run modern, commonly used browsers and keep your device secure.