I'd love to give this a 5-star review, but I simply cannot.
The developer has recently stopped providing support for versions of Firefox prior to 57 (Quantum), which also includes the latest Waterfox version (56). As such, the most-recent version of the add-on for versions prior to 57 (31.2.3) does not have support for multi-process. As such, you have to disable it to make the add-on work.
If the developer is willing to provide an update for 31.2.3 to fix the multi-process bug, I will amend this review accordingly. In fact, I'd go as far as to say that I'd be willing to donate specifically for this to be done, so long as I could be guaranteed that donating would go specifically to this end.
In the meantime, I will have to make do without multi-process.