Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

I have no idea what ANY of that means. I also had no idea my question had been answered, because I was coming here to ask it again. Also, why is THIS page moving right and left? Is it my Mac Magic Mouse?

Anyway, when writing emails, Facebook messages, or eBay messages, they'll just suddenly DISAPPEAR, POOF! It's totally nerve-wracking. I hate to give up Firefox, but I may have to.

Did you read the Safe mode article?

Such issues can be caused by an extension that isn't working properly.

• https://support.mozilla.org/kb/Safe+Mode

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

See also:

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes