Firefox: "The connection was reset" on some sites

If it happens that on some websites you get "The connection was reset" (like this one), but the the websites work under Opera or Windows, it could be that you are running Firefox in Ubuntu Feisty. The fix is simple. Within Firefox go to the following address:
about:config
In the "Filter" text field type
firefoxcomment
Now, you should see a preference called "general.useragent.extra.firefoxComment". Right click on it, and change the value from
(Ubuntu-feisty)
to
(Ubuntu)
Now you are done.

This happens when the website you are trying to access blocks clients that have the string "ist" in their User Agent string, because the firewall thinks your computer is infected with the ISTbar adware.

Links of interest
Ubuntu Forums post
Launchpad bug report