Many web pages with fixed formatting do not fit on my screen without scrolling left to right. I suspect that in some cases the web page attempts to determine my screen width and adapt to it, but fails because I use a 125% or 150% zoom factor.
Some time ago, Opera had a simple command to override all preformatted line widths and force text scrolling, but I haven't found a general solution since then. I looked at the question How can I make Firefox word-wrap text/plain files? which had some answers for firefox, but both the extension suggested and the .css file seem to be out of date. I couldn't find any css files in my extension folder, so either they've changed it or I didn't understand where to look.
Ideally I would like a solution for Opera, but one for Firefox would be more helpful to the community and might be easier for someone to answer.
So, how can I force an unconditional text wrap to fit my screen in Firefox? Suggestions for any browser would be considered helpful, but an answer containing a solution for Firefox is preferred.