Why would GitHub decide I can't comment on diffs?

Question

Yesterday I changed my password on our network. Now when I go to our GitHub from Firefox, it won't let me add comments to diffs (the little marker doesn't appear to the left of the line number). This seems to be only for Firefox. I logged in using Chrome and Internet Explorer and had no problem.

I'm presuming Firefox has managed to cache something it shouldn't have done, but I'm at a bit of a loss as to where to try after clearing cache and deleting cookies for the site.

Answer 1

Apparently (I found out today) this is something in github which breaks on firefox 30. Pending a fix in github rolling out, this should be added to your userContent.css

@-moz-document url-prefix(<http or https>:<your github server>) 
{ 
  .file .highlight { 
    overflow: visible !important; 
  } 
}