I'm seeing this problem myself. I did a web search and found a likely cause: some wireless providers are injecting javascript like this into each web page visited and then compressing and caching the images on that page. Apparently, this is an attempt to reduce data usage and save them bandwidth, at the possible expense of image quality (among other things).
Are you accessing the internet via a 3G broadband device? And... when you hover your mouse cursor over an image on a page, that you've visited in your browser, does a browser pop-up/tool-tip appear stating something like 'Shift+R improves the quality of this image. Shift+A improves the quality of all images on this page'? If so, then you might contact your wireless provider and see what they have to say about it.
In my case, I have a virginmobile broadband2go device and every page that I visit gets injected with this stuff. Their proxy server (IP address 1.2.3.4 ) seems slow to respond sometimes, at least in my experience. :( That's how I first noticed the problem, a series of "waiting for 1.2.3.4..." status messages reported by firefox.
I'm not a fan of ISPs altering the programming of 3rd-party web pages that they deliver to their customers. Is this practice even safe? Could it be exploited by nefarious types?
In any case, It would be great if Norton Internet Security could detect when an ISP does this and at least give an informative warning!
Thanks
fp
P.S. I can provide URLs to other forums reporting similar problem, if requested.