I never had that, but then again, I never used what I think is currently the
latest version; I stuck with 4.9.2. Now I use NoScript because it's a lot
more powerful and less buggy (I especially can't stand that LibreJS has an
annoying tendency to split text entry boxes into more lines) and LibreJS
doesn't actually do a good job finding out if scripts are free in practice,
so it doesn't really do any better than NoScript. The annoying hassle of
having to disable LibreJS any time I wanted to reply to a forum post. The
only reason I stuck with LibreJS at all was because of a bug in Firefox 20
and below which caused the video player elements to not show up if Javascript
was disabled or blocked by NoScript.
So in short: I really recommend you use NoScript instead of LibreJS (but
change the preferences; it whitelists a bunch of sites that have nonfree
Javascript by default, such as YouTube, so the first thing I do when I
install NoScript is remove them from the whitelist), unless perhaps you watch
videos in Abrowser's HTML5 player.
Regarding the freezes, I never experienced that, but I didn't use the latest
version of LibreJS very much. Maybe you're just running out of RAM?
