We have a certain sizing behavior for the columns in the diff viewer

that keeps them fairly equal but allows for some additional room if one

side or another has wider content. To achieve this, we needed to set

minimum and maximum widths on each of the <pre> tags, and we did so by

injecting a <style> for each diff that we could control. This worked

well on most browsers, but hit performance problems on Firefox.
We now have a different approach to this. We no longer inject a

<style> into the document for each diff. Instead, we set this only for

the filename and revision columns (directly on the elements). We then

set styles to ensure the text is broken at the character level so that

it will always wrap if needed, for lines of any size.
This does result in a behavior change. We formerly would break at the

word level, breaking on the character level if hitting the width

boundary, and wrapping text to the next line (to help with readability)

if possible. We no longer have that option (we could enable this just

for WebKit, which supports the non-standard word-break: break-word, but

this creates an inconsistency that isn't worth having -- note that

word-wrap: break-word does not exhibit the same behavior in our case).

The upside to breaking at the character level is that it's easier to see

spaces that might get lost in the wrapping. We'll see if people complain.

Tested that resizing logic worked correctly and that column sizing was

working the same way as it did with the old logic.
Tested that Firefox no longer had the same slowdowns on larger diffs that

I was reproducing before.