UPDATE: If you are slipstreaming under Windows Vista then you should read this update.
Note: This process is not suppored by Microsoft. Also, it's experimental and things can go wrong. It's advisable to test your slipstreamed ISO using Virtual PC or other virtual machine package before deploying.
Yes, but this isn't as straightforward as you might imagine. This is because you can't use the normal installation executable, and instead have to download a .cab file of the relevant version of Firefox. You can find links to .cab files for Firefox 220.127.116.11 here.
Once you have the download you can proceed with the slipstreaming. When at Step 7 of the slipstream creation process, make sure that you select the Hotfixes, Add-ons and Update Packs option.
Then, when asked for the hotfixes by nLite, point the program to the installation package.