Sounds a like corrupted install did you update or update a different FF before this? You should match the latest FFx64 with W10x64 when reinstall FF. I seen when you had a x86FF the new FF will be FFx64 matching with the O/S. This will cause unforseen problems.

1.7GB doesn't sound like a lot to me if you have many tabs open. However, if you completely exit out of Firefox, then all memory should be released. Is that not happening for you?

By completely exit, I mean using the menu command, either:

• "3-bar" menu button > Exit
• (menu bar) File > Exit