Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies
  Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

Thank you so much for responding. I have cleared cookies, cache, active logins, and viewing and download history. In fact, I clear them every night as a rule. I also run CC Cleaner on a regular basis. Personally, though I could be wrong, I think the problem is related to the fact that Firefox no longer supports Java Script, and based upon all of my research, Java Script is a necessity for sites to run correctly and for certain features, like drop-down menus, to work properly, as well as for ads to show, and as I mentioned before, the ads no longer show on Yahoo Mail. Nor, for that matter, do they show on my blog when I view it or on most of the sites I visit. Yet, when I accessed Add-ons and Extensions, it would not allow me to update Java Script. It says that Java Script is no longer supported, or something to that effect. I just know that I much prefer Firefox to other browsers, but this is getting really aggravating. Last night, in fact, it was worse. I could barely do anything in Yahoo Mail, and after a while I simply gave up, went to Internet Explorer, and did not have a problem at all. Ergo, the problem is definitely with Firefox. :-)

Cherokee_Woman said

I also run CC Cleaner on a regular basis.

Using external programs on Firefox is known to cause issues. FF settings can be set up to do this on it's own.

Firefox no longer supports Java Script

Java is an external program. Javascript is built into Firefox.

the ads no longer show on Yahoo Mail

Your settings, or an add-on, could be blocking content.

Have you tried FF in Safe Mode?

http://kb.mozillazine.org/JavaScript_is_not_Java

Make sure your Java (Not JavaScript) is up to date Verify Java and Find Out-of-Date Versions {web link}

Version 8 Update 65 Release date October 20, 2015 http://java.com/en/download/manual.jsp

Hello Fred, and thank you for responding once again. You are very patient, and I appreciate your help.

First, since I am not especially computer proficient, how can running a program like CC Cleaner cause issues? It has been my understanding that CC Cleaner is a "good" program, and I have used it for years without problems.

Second, I know you think I'm a real "dummy," but I really don't know anything about settings for add-ons. Could you perhaps recommend a good site where I might learn about them?

Third, no, I haven't run Firefox in Safe Mode, because I don't know how, and, plus, I'm afraid that something might go awry if I even attempt it.

Fourth, doesn't Java automatically update or at least send those little "update now" messages? When I get one of those messages to update something, I do. On the other hand, Windows automatically updates, as does Kaspersky, without my having to do anything.

Finally (Are you breathing a sigh of relief? :-) ), for some strange reason when I logged in to my Yahoo Mail a few minutes ago, everything was working as it should. The drop-down menus were back, as were the ads. However, this anomaly, for want of a better word, happened a few days ago, but the next time I logged in to Yahoo Mail, nothing was working as it should. Isn't that rather strange? Why would it suddenly be all right but then, just as suddenly, be messed up again? Do you have any ideas?

Thank you again, Fred.

Cherokee_Woman said

how can running a program like CC Cleaner cause issues?

By removing the wrong files. Firefox can, if needed, do that on it's own.

I know you think I'm a real "dummy,"

Once upon a time, I was here asking questions. Now, I answer them. Some day, you can do the same.

I really don't know anything about settings for add-ons. Could you perhaps recommend a good site where I might learn about them?

You can ask general question here. Harder questions you can take to it's support site.

I haven't run Firefox in Safe Mode, because I don't know how, and, plus, I'm afraid that something might go awry if I even attempt it.

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

doesn't Java automatically update

Yes, but sometimes the update does not work. Or, it forget to check.

for some strange reason when I logged in to my Yahoo Mail a few minutes ago, everything was working as it should

Sometimes, the problem is a corrupt file that was overwritten. If the problem is gone, Great ! !

Fred, I cannot thank you enough for being so patient and for taking time to respond to my questions in such detail, as well as language that a layperson like me can understand. I truly appreciate it, and I mean that sincerely.

The strange thing is that when I logged-on tonight and went to Yahoo Mail, once again everything was working as it should. You said that a "corrupt file" could have been causing the issue, and maybe that was the case, though I can't help but wonder how the file suddenly ceased causing a problem if it was corrupt. (Picture me looking befuddled. :-) )

The only thing different that happened prior to Yahoo's suddenly behaving was that I received 28 updates from Windows on Wednesday night. Could one of those updates have resolved the issue?

Then again, the next time I go to Yahoo Mail, it could be "wacky" again, but I'm not going to allow myself to consider that possibility, and instead try to think positive.

Again, Fred, I really appreciate your help. You are very knowledgeable, and I want to thank you for being so generous as to share your knowledge with me. I hope you have a nice weekend.

Without looking at whatever file was causing the problem . . . . . . Good luck and safe surfing.