It's pretty broken now, even with a new profile. Not surprising as JavaScript gets updated and more sites depend on the Google crap and customElements. Too many sites also only target the last 2 releases of a limited set of browsers. Reading the SeaMonkey newsgroup, it's a problem with the latest releases on quite a few sites, even some like Youtube which still works fine here, as well go browsers such as PaleMoon Brave and other forks.
SeaMonkey's newsgroup is now at alt.com.software.seamonkey, Firefox and Thunderbird are nearby as Mozilla has dropped their newsgroups.