No, not really seeing memory leak through memory usage appears higher than previous versions. Firefox is releasing memory, slow in my case. In fact, seeing 603MB with 2-tabs open, one being media heavy. In Chrome, which is also open, I'm currently using 1,500 MB. Though on Adobe Max streaming webinars all day, not really surprising? BTW, Adobe Max is free this year, which ends today. Many of the workshop sessions will still be available on-demand. Helpful expert tips if you are using Adobe CC apps.
Are you using any Firefox add-on/extensions which can be a source of memory leaks? You can try restarting in 'Help > Restart with Add-ons Disabled'. And check if memory leaks still exists?
Also, modern websites rely heavily on media and scripting, and poorly written scripts in particular, can result in browser memory leaks.