Mike Fabian asks:
I've never seen that in Mozilla and couldn't reproduce it now either. Where exactly does that happen? In the URL entry widget?
No, in the Subject box of Mozilla mail. The URL entry thingie of the browser component is fine.
Is it reproducible? Can you give detailed instructions how to reproduce it?
I'm afraid that you're going to have to use (or at least be about to use) Mozilla mail. Type something in the "Subject:" box. Move the cursor to the start of the resulting line of text. Hit delete a few times. You'll get a kind of mess where the characters were at the end of the string, so what was World domination and should now be ld domination is now ld dominationnnn or similar (the phantom characters at the end are sometimes clear, sometimes not). Now move the cursor outside this line (e.g. to the message area) and the mess may or may not disappear. Could this perhaps be font-related? No, probably not -- I'm not aware of ever having consciously chosen a font to use in that part of Mozilla, but anyway it's a sans-serif monospaced font, very unlike the serif monospaced font in which I'm now typing this. The former seems to be the same font that's used for the menus of Mozilla mail and the Mozilla browser ("Go" "Bookmarks", "Tools", etc.), and for the URL window of the Mozilla browser. Ah, it's probably just some Mozilla buglet. I'll learn to live with it for the short term. (In the medium term I think I'll change mail client, for other reasons. But I have to learn some other aspects of Linux, not to mention attend to Linux-unrelated concerns, before I get around to that.)