Two good sites for themes are:
MozDev.org Themes
Seamonkey Add-ons Themes

You can download Mozilla here. It is a In-Development Browser without support, so if you need support then I recommend you get Netscape or another Mozilla Based Browser.

Users can download SeaMonkey from here.

The SeaMonkey project is a community effort to deliver production-quality releases of code derived from the application formerly known as "Mozilla Application Suite".

User support for Seamonkey is available at the MozillaZine SeaMonkey support Forum

Yes, there is a project called Googlebar that preforms the basic functions of the Google Toolbar. I does NOT include Google Compute. If you wish to Fold/Crunch like Google Compute does then you can find instructions here.

Yes.
Bugs can be passed on if you do not uninstall your old version before installing your new one.

EDIT: Upgrade to Mozilla 1.3 because it's alot faster.

Mozilla is known for loading pages slower than other browsers. Here is a little easy setting to change to make it faster.

Goto edit-preferences-advanced-HTTP Networking, and hit the two checkmarks for "Enable Pipelining"

If you download new Mozilla builds frequently, it is advised that you occasionally delete the Mozilla Registry. Although this will erase the record of where your Mozilla profile is located (the profile itself will remain intact), it helps to prevent problems from old registry files being incompatible with newer Mozilla builds. If you experience a crash on startup problem with a fresh Mozilla build, deleting the registry file will might resolve this. It sometimes even allows newer features and fixes in Mozilla to work. This is partially why that it is not recommended that you use Mozilla as your permanent browser. The filenames for the registry files are listed below:

Mac OS - Mozilla Registry in Preferences under System Folder. If present, also delete Mozilla Versions.
UNIX - registry in ~/.mozilla/
Windows - mozregistry.dat, and mozver.dat if it is present, in Windows or Winnt.
If you intent on using Mozilla frequently, and especially update to newer builds once every few days, it would be wise to back up files important to your Mozilla profile. Especially, keep an extra and updated copy of your bookmarks file, and take other precautions to avoid lossing important information! Although Mozilla is stable enough to use on a regular basis, switching to newer builds might bring in significant problems with that build. For example, there was once a bug that caused the entire bookmarks file to be deleted, forcing developers to remove that build to from the server (the only instance that I remember a build being removed), and a new build was quickly released with this problem resolved. Although this was a very rare instance of a very damaging bug, it was unexpected for those who were unfortunate to download that build before it was removed from the server.

Linky is a very simple add-on to the context menu that provide you with the following:

* Opens all links in a selection in new tabs or windows
* Finds and opens link in plain text in a new tab or window
* Opens all links on page in new tabs or windows
* Open all links that appears to be linking to an image in new tabs or windows
* Shows all links that appears to be linking to an image in one new tab or window
* Open all links that appears to be linking to an image in one new tab or window

It can be found here.

CHECKY 0.5.1 for Mozilla and Netscape

The Checky plug-in is a simple Interface for web content and resource developers to free and commercial online Validator and Checker services.

With Checky you can now easily set-up, combine and use 18 different online Validator and Checker services. Simply choose your services with Checky-Agent, then browse to web resource and press F10 to display the results of the selected services in a new browser tab or window.

More information can be found here.

Search for all Mozilla shortcuts on your computer, right click, select properties and in the target line directly after the quoted string place -nosplash include a space after the sting target location then close the properties dialog box by clicking on the okay button. Shut down then re-open the browser for this tip to take effect!

Block all those popup ads. To disable popup windows, select Advanced and then Scripts & Plugins from the Preferences window. Then uncheck the box that reads "Open unrequested windows".

Credit DSmithLady