You have accidentally hit the "insert" button to the left of your numbers keys - go up and click 'insert' again and this will stop.

no I never use that, but I have tried that button. I think is some kind of malware thing.

Have you tried rebooting?

Agreed always try a reboot first. Is this happening every where you try to type or just in email? When you reply here for example is it happening? Another quick thing to try if a reboot doesn't help might be a system restore to a date before it started happening.

Start, accessories, system tools, system restore, restore your computer to a previous date, select date from the dates available in the calendar and restore.

But tell us where all its happening.

And of course running a malwarebytes free scan is always a good idea. But I don't think this is an infection issue unless there's other problems with it.

To me it sounds like a software bug. By that I mean that XP is very old and no longer supported by Microsoft so Firefox and some of the other search engines may not be supporting it either when they write up their updates. Firefox may have done an incompatible update and corrupted the function you're having problems with. I hope I am wrong, but if that is the problem, you may need to finally upgrade. Do you know how to take screen shots? I would take some screen shots of the issue if you do. I would also go to the Firefox site to see what kind of support is available and go from there. I just saw this there, maybe someone in the Firefox forum has a solution

Firefox help section

I have XP and up to date Firefox and no issues. While MS has disavowed Firefox, it's still the most used OS on the planet and most software providers are currently sticking with it. A notable exception is Java, but they've had so many security problems that it's no wonder.

I would urge everyone to upgrade their windows to a more current version than XP.

With Microsoft no longer supporting it, viruses and other malware can cause issues and you won't get any patches from Microsoft to fix exploits that are discovered.

But the current Windows formats are awful and I have good security (part of which includes a suspicious nature), so I'm not going to do that. I will eventually need to update my hardware, and at that time will evaluate 10, Apple and Linux and see if I can stand any of them. Many businesses, which are notoriously leaky, have no intentions of changing from XP for many years. They have customized software and will only change when the situation is dire.

JoAnn, any luck?

It just occurred to me that Summer could also be a problem. Have you dusted recently? Try putting an old stocking or other mesh over your vacuum's crevice tool if you don't have a computer vacuum. Go over the vents well, and if your computer is the kind that opens up, gently dust inside the case as well. If you use canned air on the more stuck in spots, make sure that you're blowing fluff out rather than further into the crevices. A plastic tipped tweezers can be useful. Heat and dustbunnies (which trap heat) can do a number on the function of a computer.

When you left-click, does it highlight a word or two, a whole line, a whole paragraph, or every word in the letter?

Does it happen every time or just often enough to be annoying?

Does it also happen in this reply box?

If it's one or two words, a line, or a paragraph, doesn't happen every single time, and also happens here in this reply box, you might have a dirty left mouse button.

A dirty left mouse button could give you inadvertent double/triple clicks causing highlighting.

Just a guess, something else to try perhaps.

Its still doing it but I don't think as bad or I am getting used to it. It will do one word, or or a paragraph at a time. It does it everywhere but mostly I notice it in emails. still scratching my head.

how do you clean a mouse anyway?

I just used a cleaning wipe on it and so far is seems to be working. My next letter should tell me more. Thanks

Might be time for a new mouse, as cheap as they are now.

I don't know of an easy way to clean the buttons.

When I had a mouse button go bad, I'd click a shortcut in my taskbar and the program would often times open up twice. And while trying to drag an object to a new location(such as the trash can), the button would lose contact and I'd drop it some place I didn't want it. The solution for me was a different mouse. Not a new one, just a different one.

Where is this happening? In a Word document? In Outlook? On this message board?

I found this solution for a highlighting problem:

http://thecyberdaily.com/2011/08/mouse-highlights-everything-when-i-click/