Check your plugins:

• Plugin check

Try clear your recent history

• Clear recent history

This happens in safe mode?

• Firefox in safe mode

Also:

• Problems with malwares

Could you be more specific about the problem you encountered? For example, did the login page load? If so, did you log in by hand or did you have Firefox or another password manager log you in? Did your Inbox load partially or did you get an error message? Are the styles messed up or icons missing? These kinds of details would be helpful in diagnosing the problem.

Meanwhile, a couple of thoughts:

(1) Yahoo has been updating its users to a newer interface and this may involve a change of server. If you are using an old bookmarks or old home page address to access your mail, try going through the Yahoo home page instead.

(2) If you haven't already, 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.

(A) Bypass Firefox's Cache

Use Ctrl+Shift+r to reload the page fresh from the server.

Alternately, you also can clear Firefox's cache completely using:

"3-bar" menu button (or Tools menu) > Options > Advanced

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

If you have a large hard drive, this might take a few minutes.

(B) Remove the site's cookies (save any pending work first). While viewing a page on the site (anywhere on yahoo.com):

• right-click and choose View Page Info > Security > "View Cookies"
• Alt+t (open the classic Tools menu) > Page Info > Security > "View Cookies"

In the dialog that opens, you can remove your Yahoo cookies without affecting other sites.

Then try accessing mail again. Does that help?