== The issue ==
Search and text selection highlighting visuals get mismatched with the actual selection in view-source when the value of `layout.css.devPixelsPerPx` is 1.2 or larger.

== Steps to reproduce ==
* Open `about:config`, find `layout.css.devPixelsPerPx` and change the value from default (-1.0) to 1.2.
* Open a view-source view with long lines: `view-source:https://www.youtube.com/user/10asti10`
* hit Ctrl+f, search for rss
* using the LMB, try selecting some text, then copy and paste it somewhere

== What happens ==
Screenshot 1: the highlighted text on the page is not ”rss”. The highlight doesn’t even adhere to letter widths.

Screenshot 2: the pasted text is not even close to what you’ve selected to copy.

== What I expect to happen ==
For the search to hightlight an occurence of ”rss”, and for the pasted text to correspond to what I’ve selected from the view-source view.

== Other info ==
* In my testing, a devPixelsPerPx value of 1.1 seems to not trigger this, whereas 1.2 and anything above does.
* In addition to 18.04 (whence the attached info is from) I’ve reproduced this in a VM running up-to-date 18.10.