Rated 3 out of 5 stars
Useful, but still problematic and frustrating. It forces Tor to be the default proxy, and the option to set your own default proxy is summarily ignored (the option of selecting a default proxy is provided, but doing so is either broken or is deliberately forced to be Tor, I can't say which).
The UI is also pretty awful. Adding the first rule is rather problematic until you get one or two to finally stick, and the wildcard method of adding web addresses is generally pretty good, but it is sometimes ignored.
In short, this is a long way from Switchy on Chrome, but it's the only automatic proxy switch that I can find for Firefox here on Mozilla.org. It only gets the job half done because it forces Tor (and I would prefer to default to i2P), but it is better than nothing. At least I can still easily connect to eep sites, and I can still route certain domains through a proxy.
This plugin also takes over the Network configuration window under Firefox's Options : Advanced : Network, which is a little irritating.