Spybot-S&D does also support other browsers than Internet Explorer. It can empty the browser's cache and history as well as checks for bad cookies, start page and bookmarks. As for resident protection Spybot-S&D contains the Resident TeaTimer which is completely browser independent. It is a Spybot-S&D tool perpetually monitoring the processes called/initiated. In addition, TeaTimer detects changes to some critical registry values.

But what about the Immunize feature?

Firefox
ActiveX isn't supported by Firefox, so there is no need for protection there. Maybe in one of the coming versions there will be a bad download blocker for Firefox, but not at the moment.

Netscape
Please run Spybot - Search & Destroy in "Advanced Mode" and go to "Tools" --> "Hosts File". Here you can block specific internet sites known for bad behavior (mostly sites installing spyware or tracking functions). This should be the best protection if you are using Netscape browser.

Opera
Spybot-S&D does also support the Opera browser. The list of blocked installers in the resident section shows all Opera profiles, and how many of the plugins that Spybot-S&D knows as bad are already blocked in each profile. To set the complete protection, just tick the checkbox in front of the profile you want to protect. To remove the protection, untick the checkbox.
There are not many browser plugins working working for Opera currently, but the attempt to install some may crash Opera, and ActiveX support for Opera is available in third-party beta software, so use this function as a pre-caution against future misuse of Opera through spyware.
This feature will (certainly) only be displayed if you have Opera installed on your system!

Spybot-S&D supports detection in cookies, history, start & search pages and bookmarks of these browsers (plus cache for Internet Explorer and Opera):

• Beonex Communicator
• Firefox pre-0.9, 0.9, 1.x, 2.0 and compatible, including old Firebird variants
• K-Meleon
• Microsoft Internet Explorer 5.0, 5.5, 6.0
• Mozilla Suite
• Netscape Communicator 4.x, 6, 7
• Opera 4.x, 5.x, 6.x, 7.x, 8.x, 9.x and compatible
• Thunderbird 1.x and compatible (where applicable)