Hello Brian, occasional slowness (or slowness in certain stages of loading the Facebook timeline) is normal. Just let it load completely before you start to scroll down. Facebook and other heavy websites are programmed to run on computers 10 years younger that ours, so we need to be patient sometimes (or buy an Intel Mac).
As for the crashes: this is not normal. I'm a regular Facebook user, and the release versions of TFF 38 have never crashed even once on my three G3/G4 Macs running 10.4 and 10.5. Can you attach a crash log here?
Open Console (Applications>Utilities) and navigate to Log Files> ~/Library/Logs> Crash Reporter> firefox_2015XXX.crash.
Then copy & paste the contents of the right window to a text file and attach this to your post here (or just copy the contents into a post directly, even though this makes for very long and unsightly posts).