Thanks: as I'm not familiar with that site, didn't know "www." would be needed before the rest.
Using the latest Firefox 158.0.1 on Windows 10 22H2, it seems fine at different zoom-levels, from what I can tell (as I say, I've never used that site before to know what "normal" would be):
I'd suggest one of a few things you could try:
First, make sure an extension isn't causing this issue. Tap ALT to show the old menu-bar, then click the Help menu and look for either "Safe Mode" or "Troubleshoot Mode". Test the site in there and if zoom-in and zoom-out work correctly, an extension in your usual mode is causing the issue.
Second: tap ALT then on the "View" menu, make sure "Page Style" is set to "Basic Page Style", then on the "Zoom" option, by-default "Zoom Text Only" should not have a checkmark by it. However, you could try turning that on, and see if that helps (then only the text will get bigger, not graphics).
Third: if nothing helps, it may just be that the site has code too-new for Firefox 115 ESR to support; remember the ESR versions only get security-updates, but no engine updates, so eventually sites will stop working in them. As the 115 ESR is currently set to only get updates until late-March next year (unless Mozilla announce another extension), then you might want to look into "Supermium", a port of fairly-recent Google Chrome versions back to Windows 8, 7, Vista and XP:
https://github.com/win32ss/supermium/releases
There's also Pale Moon, which looks like a very-old version of Firefox, and thesedays uses
a different engine (so may cause issues on some sites -- but it has a "portable version", so
you can unzip it to a folder, and so easily test it without doing an install):
https://www.palemoon.org/download.shtml
