You need to speak to customer services as the connection that you are paying for is 8Mb unlimited. You will probably only need the 1Mb connection with a 3Gb download limit at £14.99. However there is no minimum contract with Virgin so I would look at Tiscali at £12.99 or ask your neighbours what they think of their providers. just because someone recommends a provider does not mean that they will work well at your line.
The speed of connection depends on the distance from your exchange and many other factors so 1Mb may be all you can get. I live in a small village that has an 8Mb connection 5 miles away on a large, new estate they can only get 512K....mind you I live behind Princess Anne's gaff and I'm sure this has nothing to do with the speed of the connection;-))
You can use leaving Virgin as a lever to get them to reduce your monthly cost.
Someone will answer your Firefox questions as I use Internet Explorer with Avant additions and cannot be bothered with Firefox as it is dull.