Try another browser. I recall running into a similar problem with an old v of FireFox a year or two back.
I had tried Firefox and Safari before asking. Chrome displays the page. I'd thought that Chrome and Safari had the same underlying web engine (which is why I hadn't bothered to try it earlier). Has that changed?
Different versions of Safari, some of them not all that old, have different HTML5 scores for how well they render some code. Besides old FireFoxes, another time when I ran into this issue, I was using the latest version of Safari supported on an old OSX version which I ran on one machine to work with FP5 files. Switching machines to one with a newer OS/Safari solved it, much to my surprise.
My oldest OSX still in us is 10.6.8 with Safari 5.1.10, and it rendered the latest FM updater page OK, as do the newer versions on my other machines. I quit bothering to update FireFox when it conflicted with a web-based email viewer I had used for a decade; switched to Safari completely (except for website testing).