I got a list of proxies. Some from Egypt, some from Italy, etc.
Say I want to use a certain proxy. One way to do so is to go to Tools → Options bla bla.
Is there an add-on that make this faster?
I want to see how a site looks in some countries.
FoxyProxy (source: AMO; click images for larger variants)
You setup your proxies once by picking them from a list and assigning them a color. Then you can switch easily via a dropdown – or even have FoxyProxy switch them automatically based on hostnames or other "patterns".
I've used it for quite a while some time ago, and really liked it. Didn't make any trouble, but simply did its job smoothly. Really recommendable.