By far the easiest way to get involved to to submit problems you find with SBA. Try to be descriptive but if you can't find the details don't be afraid to post, we'll try to help you track them down.
Submitting issues is fun and there are more issues on the newest versions of autosizer. Look for the packages in the download page and try the latest releases.
A great way to hear about new packages that are out for testing is in our Google Groups mailing list. Here you will be notified about new versions and you can participate in general discussion about SBA.
If you would like to contribute simply make the changes in your git repository and generate a patch. The best places to put patches are on the associated issue or in the mailing list (attachments are supported). That way we can have a discussion about the patch.
You can also try sourceforge's fork and merge feature. I haven't tried it myself but I will respond to pull request from it. Let me know how it goes.
There aren't many docs that we need but if you are ever unsure of what a setting does ask about it in the mailing list and feel free to update the wiki with new information.
Does Searchbar Autosizer not speak your language? It doesn't have to be that way. Simply pull down a copy of the git repo and add or modify that l10n files located in chrome/locale
to suit your language and submit a patch (see "Submitting Code"). If you aren't a code monkey that is all right, if you need help at any step of the way you can use the following resources.