Next to the usual proxy update, this commit also contains an algorithmic change:
Since Firefox doesn't seem to make use of the proxy fallback mechanism (try the next offered one if the previous one failed) and always uses the first one, previous editions would require proxy updates whenever the first proxy on the list failed. I've now changed the function to rearrange the list of offered proxies randomly on each request.

Advantage: A single proxy-failure will no longer cripple the script. Since the used proxy changes on almost every request, dead proxies will only lead to intermittent errors, GS as a whole will still work.
Disadvantage: Intermittent errors if singular proxies are dead. Previously, it was all or nothing - either it worked, or it didn't. Now, you should be able to get it to work most of the time, but dependending on the number of dead proxies, the GS user experience might suffer. Even for non-dead proxies, streaming quality might change randomly (literally) between songs, because of different proxies used.

Despite the disadvantages, I consider "still working most of the time" better than "just plain broken", hence the change. Please do report if this change leads to any issues with GS.

I have left the script reporting the entire range of known proxies, so browsers who do use fallback should still fall back as before, just in a different order every time.