Firefox displays each paragraph in a plain text file (txt format) as a single line, if long running off the right side of the window. That doesn't seem optimally useful.
I asked for help on it at MozillaZine forums and got the advice to right click on the page and click View Page Source, which has a word wrap option. That works, but it seems unnecessarily complicated. I wanted the text displayed in a better format in the same tab it was opened in, in one click or less.
txt to html v6
Just cut and paste the above paragraph into the "Location:" field of a bookmark "Properties" window, open a txt file, click on the bookmarklet and watch it do its magic.
The only problem I've found using it is that when it's used on ordinary web pages, it strips most of the formatting, and when used extra times, it adds extra line breaks. That is, it's not foolproof. But you can just hit the "back" button to fix any problem.
Regarding this as an example of the increasing complexity of civilization: I find a lot of humor in it, how complicated it gets to deal with the simplest formatting issue within the complexity of modern communications. If it keeps going this way, pretty soon many common formats will be almost useless, like scrambled cable, when not viewed on matched devices and software, and too tricky for anyone to crack, not because they will be designed for copy-protection, but inadvertently because of rampant complexification.
Updated May 16, 2012: More efficient word wrap bookmarklets were provided by Mardeg at Bugzilla@Mozilla forum in 2009. Either of these is what to use if you just want to change the view mode of an unformatted page displayed in Firefox to word wrapped temporarily, without changing the font or other page data:
shorter "Wrap" bookmarklet
even shorter "Wrap" bookmarklet
Mardeg also provided an undo which works for either of the two bookmarklets above, since the back button doesn't undo them:
By contrast, the "txt to html" bookmarklet I wrote mungs an unformatted page such as a txt file of plain text into a quirky minimalist html formatted page, which will then be displayed word wrapped by default and in your browser's default html font, and which you may then save as an html file. The "txt to html" bookmarklet doesn't seem to require a "refresh" bookmarklet because Firefox seems to treat rendering the newly munged page as navigating to a new page, which results in the back button having the effect of undo. I use the word "mung" since rather than convert the page data in a standard way, it's a work-around that strips the page data using the ill-advised "=document.body.innerHTML" trick and crude string manipulation, and I use the words "quirky minimalist" since rather than following standards for complete html formatting as determined by w3c, I merely used the minimum of tags that seemed to work for the purpose.
So if you use the "txt to html" bookmarklet and save a page you're viewing that way, be advised that it will insert the tags <html> <head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> [or some such according to whatever format and character encoding Firefox sets as the default] </head> <body>, a <br> for every blank line or end of line in the original, added line breaks that divide resulting lines over 132 columns into max 72 column lines [only visible in html source but done by Firefox when saving as html, maybe for backward compatibility with older text editors], and the close tags </body> </html> into the saved page.