I want to try building the gecko driver from source. The code is located in Mozilla repo here: https://hg.mozilla.org/mozilla-central/file/tip/testing/geckodriver
I downloaded tortoise svn and tried to use this URL and also the root URL in the SVN browser but it cannot parse it.
I am not familiar with SVN. What is the correct way for me to pull the code locally?
This is a Mercurial (hg) repository, not Subversion (SVN). TortoiseSVN is a Subversion client and does not support Mercurial.
You need to use a Mercurial client with this repository. Try TortoiseHg.