"If you are using the Mozilla Mark(s) for the unaltered binaries you are distributing, you may not charge for that product. By not charging, we mean the Mozilla product must be without cost and its distribution [...] may not be [...] tied to purchasing a service"
IANAL, but Dell is free to charge for the installation, but then they need to call it the Arctic Bear Browser.
[1]: http://www.mozilla.org/en-US/foundation/trademarks/policy/