Another CSS alternative exists (an alternative using CSS to address this horizontal-scrolling problem).
duplicate perl environments uses <pre> tags, which are a longstanding problem, not just in PerlMonks, but just about everywhere. If it's a big problem you could specify in your CSS that pre blocks should be constrained to a maximum size, and should be scrollable.
How-dy! It ought to noted that few formatting mishaps on Perlmonks are as irritating to me (and considerable other users) as long-line posts (horiz. scrolling). The <pre> tag is indeed deprecated at Perlmonks, but is it a reasonable expectation that most users without long experience here will remember that? Plus, is it (apparently) true that users diligently check the markup they are using against the Monastery guidelines? Point taken perhaps without me going on and on about user behavior ...
A code solution always seems attractive when one can be found. Here's one for the PRE problem on Perlmonks nodes:
The pre-wrap is defined at w3.org as doing:
This value prevents user agents from collapsing sequences of white space. Lines are broken at newlines in the source, at occurrences of "\A" in generated content, and as necessary to fill line boxes.and is from the CSS Level 2 spec.
I am not on the inside wrt nuts and bolts of the Everything machine and the production of markup on PMo. So I have to leave it to someone else to work out the best way to actually implement the application of a default style setting (that is different from the default in most user agents). But a simple approach would be to just change the Common CSS for all Themes.
I run two CSS sheets in my Perlmonks reading / posting which I do consistently using only FFx (Firefox). One was nicknamed "NYPM Blue" by me a long time ago and is set up in User Stylesheet Settings in Settings. The original 6 Themes include the Dark theme which I have toggled in User settings. So the Dark theme is CSS-cascaded previous to my custom NYPM Blue sheet. I've got the NYPM Blue sheet housed at https://github.com/somian/FFx-userstyles. You, the public, can look for yourselves.