Do you recall disabling any JavaScript related features using the QuickJS extension? If so, you could check on whether re-enabling them helps with Yahoo.

I notice you have a couple of Yahoo-related plugins. Starting in Firefox 30, less common plugins were switched to "Ask to Activate" so sites need your permission to use them. This might be confusing Yahoo.

To test this theory, could you try switching those plugins to one of the other options:

• Always Activate - all sites can use the plugin without specific permission
• Never Activate - no sites can use the plugin (unless you give them permission through the Permissions page of the Page Info dialog while viewing the site)

To make this change open the Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. I suggest trying "Never Activate" first. When visiting Yahoo mail again to test, you can use Ctrl+Shift+r to reload the site fresh from the server (bypassing cached files).

No luck. I don't recall disabling any JavaScript features. I wouldn't even know how to do so.

I changed all the plug-ins to "never activate" and then restarted FF. When I did, all the plug-ins came up again as "ask to activate." I also tried changing them to "always activate" and had the same experience.

I then tried to refresh Yahoo mail using Ctrl+Shift+r and got the same page that was there before.

The problem seems to be caused by FF 30.0. I didn't have a Yahoo mail problem with earlier versions of FF and I don't have one now with IE. I appreciate your help, but changing settings didn't change 30.0, and that seems to be the cause.

If you lose your settings change when you exit and restart Firefox, this can be caused by a user.js file among other reasons (your system information doesn't show one of those). See: How to fix preferences that won't save.

It also can be caused by software that protects you from settings changes by rolling them back. An example of that is Advanced SystemCare ("Surfing Protection" feature).

I tried resetting FF, among other things. At the cost of losing some of my preferences and add-ons and having to reload them, that reset brought up a slightly different version of yahoo mail that wasn't much better. Unlike the earlier version, it shows the options for Delete, Reply, Reply All, etc. But like the earlier version, there is no option for changing settings, the appearance is less attractive, it doesn't add my signature to outgoing mail correctly, and so on. The problem seems to be inherent with FF30. That isn't the case when using yahoo mail from IE or Chrome.

Hi Dennis, for what it's worth, Yahoo mail seems normal to me in Firefox 30.

Have you noticed any issues with other secure (HTTPS) sites since this problem began, such has having to make exceptions, or not applying styles correctly, or missing functionality?

It's very strange. No, I haven't noticed any issues with other HTTPS sites. Yahoo mail is the only thing I've had a problem with since the upgrade to FF 30, and even that works fine in other browsers. Thanks for the suggestions.

After the reset, are you at least able to change the activation status of plugins and have it stick between sessions, or is something still interfering/overriding your settings?

Nope. I tried an experiment setting one plugin to "Never Activate," then restarted FF. It popped up again as "Ask to Activate."