When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

1. Clear Firefox's Cache

orange Firefox button or Tools menu > Options > Advanced

On the Network mini-tab > Cached Web Content : "Clear Now"

2. If needed, delete your yahoo.com cookies (this will log you out)

While viewing a page on the site, right-click and choose View Page Info > Security > "View Cookies"

Use Remove as needed, then try reloading the page and logging back in.

Does that help?

Although this didn't address my specific problem (inability to open emails from people) I did do what was suggested. I have wanted to find out how to clear cookies for some time so the info was useful. However I am still having difficulty opening personal emails although occasionally I can open one. The emails I can't open are from people both new and frequent correspondents.

Start Firefox in Safe 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

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