Can you please update to Firefox 69 and see if you have problems there? 62 is no longer supported

Sorry, the new version apparently does not keep my bookmarks and logins, so I decline to use it. Kind of strange that you're not supporting a version that's just over one year old. This is a longstanding problem, for more than ten years, so the version of Firefox doesn't matter.

Versions of Firefox are considered unsupported once the new version comes out. Firefox 69 will migrate your bookmarks and data over if you're using the same profile, and it has many performance and stability fixes.

OK, how do you do it in whatever the latest version is?

Well, stopping data transfer isn't what you actually want to do. The issue is that there is some problem that is causing Firefox to stop loading a website, so we need to troubleshoot that.

Once you update, can you tell me if you're still seeing issues

No, this has been going on for years, so it's not a version problem. A website will get stuck on "Waiting for ... " or "Transferring data from ... " (gray box in lower left-hand corner). How do I stop the data transfer?

Well, let me spell it out: HOW DO YOU INTERRUPT A DATA TRANSFER?