More often than not, these kind of problems are caused by malware. I suggest in the first instance that you download the free version of Malwarebytes from http://www.malwarebytes.org/products/malwarebytes_free and run a full system scan.

You also need to update a couple of plugins. The versions you currently have installed expose your system to attack.

• Update Java via http://www.java.com/en/
• Update Shockwave For Director via http://get.adobe.com/shockwave/

Thank you for the suggestions, I will follow them.

Strange, though, that all my issues started the second I installed v. 4. Does that mean I coincidentally invited all those issues together with it? And that they all went away again coincidentally when I went back to v. 3.6. Did I eliminate all the threats with the reversal?

Other users report that their CPU usage is at 100% with v. 4, which I cannot confirm (I didn't test that), but it would explain the delay issues. Such a scenario does not look like it is caused by malware. Are these claims all made up, or are they real, and why is Mozilla not acknowledging them, if they are?

Xircal, I have now completed a malwarebytes scan (five objects had an issue, with a total of 13 potentially harmful programs, all destroyed), done the Java and the Flash updates.

Unfortunately, no improvements, and actually it got worse :now I even have these delays with FF v. 3.6.17 (this new behavior had started before I did the updates and the scan).

Now what?

Thank you for any other helpful tips you may have (including an acknowledgement that it is being worked on ;)).

Did you check your security software (anti-virus, firewall) and make sure that it isn't locking files or restricting Firefox in other ways?

Create a new profile as a test to check if your current profile is causing the problems.

See:

• Basic Troubleshooting: Make a new profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins"

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Okay, so now I am a bit confused. First, thank you cor-el for the suggestions and the links. I had always been using the default theme. I opened in safe mode: no issues. I disabled all add-ons, no issue. I enabled all the add-ons again (in groups): no issue.

So, basically, just by going into safe mode and then back to normal fixed my problem. Now I will upgrade again to v. 4 and see what happens then. Stay tuned...

This is likely my last post in this thread. I am now back on v. 4, with my McAfee scanning in the background (to get the CPU busy), and there are no delays. At least none that would bother me. Scrolling still stumbles for a fraction of a second, but that is acceptable.

So, thank you for making me go through these steps, and if you know which one fixed the problem, then you know (again) more than I.