Here's a simple trick to get rid of a little cruft in your firefox theme. Specifically, the "go" buttons next to the address bar and the quick search bar. Personally, I never use them, so I'd rather have longer input areas.

Step 1. Find the theme extension's folder

I'm running OSX, and found my themes in my Application Support folder.

$ cd ~/Library/Application Support/Firefox/Profiles/[tab]/extensions

Firefox keeps the themes and extensions in the same folder, so you may have to dig to find which cryptically named folder contains your theme. If my shell skills were a touch better, I'm sure I could spit out a one liner to output a list of folders and their respective extension/theme. In the mean time, I just do this:

$ ls -l
drwxr-xr-x    9 me me  306 Oct 13 22:47 firebug@software.joehewitt.com
drwxr-xr-x    6 me me  204 Oct 13 22:47 yslow@yahoo-inc.com
drwxr-xr-x    7 me me  238 Oct 13 22:47 {239c61a8-etc-etc-blah-blah}
drwxr-xr-x   10 me me  340 Oct 13 22:47 {3CE993BF-even-more-etc-etc}
[snip]

$ cat */install.rdf | grep em:name
                   em:name="Firebug"
    <em :name>YSlow</em>
    <em :name>TheThemeYouWant</em>
                   em:name="Another extension"
[snip]

Then I just match the dir to the name by line number. A quick double check in that specific directory's install.rdf and we have our target. In this case, I'll touch up TheThemeYouWant (yes, I made it up).

Step 2. Get the extension's css from the chrome jar

Now just change into the chrome directory under your theme's directory, and unzip a few files out of the jar.

$ cd {239c61a8-etc-etc-blah-blah}/chrome
$ unzip ../*jar browser/browser.css browser/searchbar.css
Archive:  ../why-you-wanna-change-me-0.0.1.jar
  inflating: browser/browser.css
  inflating: browser/searchbar.css

Step 3. Add a little display: none;

Now edit both files in your favorite editor. Add display: none; in browser.css here:

#go-button-stack {
  padding: 2px 0px 2px 0px;
  display: none; /* no go buttons, kthxbai */
}

and in searchbar.css here:

.search-go-button-stack {
  padding: 2px 0px 2px 0px;
  -moz-padding-end: 5px;
  display: none;
}

Of course, you could monkey with the other style rules in there as well, but this is a quick mission.

Step 4. Update the jar

Now just zip update the two files back into the chrome jar and restart Firefox.

$ zip -r *jar browser/browser.css browser.searchbar.css
updating: browser/browser.css (deflated 83%)
updating: browser/searchbar.css (deflated 80%)

After a restart, those much ignored buttons should be gone. If you hadn't just gone through all this work, perhaps you might not have even noticed.