A little extreme for first contact. Hello Firefox Support Volunteers will try to help you with your issues.

I also use this and have no problem accessing my mail.yahoo.com accounts/

uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files.

Note: your Firefox Profile is saved. But you should make a back up before you do : https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

It's not clear what you mean by this: "restores yahoo to its normal view." What kind of view are you getting? More info leads to a better chance at a solution.

If you are using an old bookmark or home page, try going through the Yahoo home page instead in case the saved address has become obsolete:

https://www.yahoo.com/

Here are some common issues:

(1) Cannot connect due to secure connection error. See:

• "Your connection is not secure" -- page generally has an "Advanced" button to get more technical information.
  • What do the security warning codes mean?
  • How to troubleshoot security error codes on secure websites

• "Secure Connection Failed" -- typically has scantier information about the problem and if the padlock appears normally, can be taken to mean "connection failed"
  • Secure connection failed and Firefox did not connect

Do not make exceptions for well-run sites or sites that handle sensitive information!

(2) Can log in but then get a blank page.

Check for the redirect block:

(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(B) In the search box above the list, type or paste access and pause while the list is filtered

(C) If the accessibility.blockautorefresh preference is bolded and "modified" or "user set" to true, double-click it to restore the default value of false

More generally, if you haven't already, you could try "the usual":

If a site is generally known to work in Firefox, these are general suggestions to try when it stops working correctly:

Cache and Cookies: 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

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?