There's a reason it's still the standard in the legal industry.
The funny thing is that Word has tons of functionality that techies aren't aware of because they don't actually use it so they keep building products around features Word has had for years. And then they wonder why their startup failed to get any traction.
Redline doesn't appear to be working in Firefox in the web demo you have available. As that is supposed to be your killer feature I would say that your product isn't yet in MVP state. Also, the UI is quite bad and not the slightest bit intuitive; it's the kind of UI that only makes sense once you already have been using it for a while. As you pointed out, most firm lawyers already know and use Litera, so you need to not just be better at your one chosen feature but you also need to be easier and more intuitive to use and you're not.
It's okay for you to be offended by this criticism; this is your baby. But I'm being realistic here. You can choose to ignore critiques and die stillborn, or address these complaints (which other comments have also pointed out) and actually make something that a small but sustainable niche of lawyers will happily use.
Agree to disagree on the UX, but points very much appreciated!
[Edit: what OS and generally what type of edit? Firefox on Windows is working, but perhaps there's a specific edit which caused it to crash. Thanks so much!]
Hard disagree on the UX. Remember that it's not what you think of the UX, it's what your users think of the UX. This is basically like GIMP or Darktable; I'm sure it makes sense to power users who have invested a lot of time, but unless you want that tiny group to be your market, you need to make the UX way more user-friendly.
I'd expect most firms to have their own systems for backup, versioning, access control, approval, metadata, etc.. or at least a human process for such. It should be much easier to sell the "extra tools" than software that changes their process.