First, and most easy, replacing the splash screen is being done by simply placing any bitmap (that's any size etc) in the root directory where mozilla is installed (usually \Program Files\mozilla.org\Mozilla) and naming it "mozilla.bmp".

When done, replacing default icons for all components isn't hard either (thanks Bosko for pointing us here). Full specs and credit to grayrest, pages here (get his cool package) and foremost here! Summarizing results a bit, it's done by placing specifically named icons at \Program Files\mozilla.org\Mozilla\chrome\icons\default. The folders named "icons" plus subfolder "default" might not be there initially, just create them. Now, components and iconname that will make those work automatically: Then, the throbber. Mozilla and Netscape 6.x share the format, it now takes (animated) .gif. One major plus is the Mac version eats those too, Mac resources provide usable throbbers (to extract .sit/.hqx files, check here). Complication, or more fun, the throbber is part of the theme/skin format (that something MS never would do :). This, practically, means the throbber is contained in one of two default themes provided, "classic" and "modern".

Now, you could take the long route and learn about theming Moz and/or theming NS. But if you just wanna change the throbber, them themes are contained are contained in .jar files (archives, (very) like .zip), path (Moz) \Program Files\mozilla.org\Mozilla\chrome\ or (NS) \Program Files\Netscape\Netscape 6\chrome\. Modern.jar (default) and classic.jar are the themes. If you extract (most compression utilities handle that), a complex folder structure enfolds. Location of the throbber differs with Moz/NS version.

For versions 6.0 of NS, we found it at \skin\"skinname"\global, files were animthrob_single.gif (static version) and animthrob.gif (animation).

For Mozilla and NS version 6.1, we found it at \skin\"skinname"\communicator\brand, filenames were throbber-single.gif and throbber-anim.gif (plus size variations named throbber16-single.gif, throbber16-anim.gif, throbber25-single.gif and throbber25-anim.gif). Mozilla doesn't have the 25 variations.

Default throbber uses 30x30 frames, but you can go a couple of pixels above and below without breaking the theme. One action left, but crucial, compress again and replace the file. Backup, it's easy to break it to do nothing at all anymore (even with the backup file in place again). Download and use FilZip for this, overall handy and complete zip utility (free, all Windows versions). Please be sure to have folder structure inside the .jar exactly as it was before extracting (this telling you it's actually a quite easy operation, but every little mistake might well break your complete install...). Note: we've found a couple of references to .css files, inside and outside them theme files (version differences, again), that provide some control over the throbber. Some require the exchange mentioned above anyhow, some don't but don't work in all versions (?). We'd like to hear about a more save/solid solution, if available, but will stick with this, as it worked :).

With Netscape builds 6+, check Mozilla info above, it's the same. For history's sake, throbber info for older builds.

They use a .bmp too (like IE), with each frame of the animation inside, but they're placed after eachother in a horizontal sequence. Common formats are 30 x 30 frames (small logo) and 48 x 48 frames (big). For Netscape 3.0x you'll need to stick to that, Netscape 4.xx allows other sizes, it doesn't even need to be square frames.

For Netscape 3.0x you just need to name the bitmaps 30m.bmp and 48m.bmp and place then at the same place where the main Netscape executable is (commonly: C:\Program files\Netscape\Communicator\Program).

For Netscape 4.xx the bitmaps can have any name. They must be put at the same place. Also you need to edit a file called "prefs.js", found in C:\xx\Netscape\Users. Find the profile you're working in and the .js file inside. Now open in notepad and add the following lines, customized to your own bitmaps. As said, name the pictures whatever you want. Count the frames you've made and set the proper value (needed to calculate the width of the animation). Also you can change the address of the webpage that will open when the animation is clicked. Last, but important, the file needs to be set to "read-only" (rightclick, properties), to prevent Netscape from removing these lines.

Latest Opera releases are very configurable, near to being skinnable. Toolbar background, toolbar buttons and more of the toolbar parts are exchangable. Info is here, as are some 'skins'. Some additional tweaks.

twisted_steel provided the steps to remove the text "Opera x.x" from the splash screen dialog, splash screen itself and the titlebar text. Splash text:

1. open opera.exe in resource hacker or other resource editor;
2. navigate to string table 1320;
3. it will say something like:
   
   STRINGTABLE
   LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
   {
   21104, "The saved windows file appears to be corrupt and can not be used."
   21111, "Opera 5.12"
   21112, "Setup files (*.win)|*.win|All files (*.*)|*.*|"
   }
   
   Replace Opera 5.12 with whatever you want, or leave it blank.
4. click the compile script button;
5. go to file/save in resource hacker.

The splash screen itself is a seperate .gif (splash.gif in Images subfolder); it needs to be 400 by 240 pixels. It works fine with a completely transparent GIF, except that a thin black border remains where the splash should be.

For the titlebar text, keep your resource editor open and go to string table 1256. It should say the following: Next to 20092 it says "Opera x." Change this to whatever you want. Then click compile script and save.

Bosko adds a tweak to change the program icon (working with 6.04+). You'll need to open Opera6.ini (main program folder) in notepad and add a line below [User Prefs]. It should read "Application Icon=path_to_icon.ico" (no quotes).