So last week I started working on a bug for PDF.js. I spoke to the developers of the library, on IRC, and they advised me to concentrate on a different bug because this particular one was an edge case and not easily implemented. So they asked me to focus on something that would be immediately useful.
Keeping that in mind I found a bug that they are trying to ship for Q1 of 2015. This bug would allow PDF.js to integrate better with other libraries Hypothesis. Although this bug seemed simple at first, I didn't know where to get started coding. I asked the developers and spent most of my time in one directory, which Yury pointed out, but I was coding the wrong file. After several hours of hacking and not seeing anything change I decided to checkout some other files. I found the pdf_page_view.js where I made the appropriate changes to meet the developer's needs.
The code made the following change to DOM of the rendered PDF:
Overall this was a great experience and the developer's I interacted with on IRC were very helpful. Thanks to Yury and Snufflepagus for the help. I am probably going to stick with PDF.js for next couple of releases.