How often do these messages come up? This is on many websites?

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Hello again,

Yes, I tried safe mode. It did not help. I'd guess it is on at least four or five

sites. I tried blacklisting javascript on those sites with another extension, but it did not help. Every day I hit three or four different sites with this problem out of a fifty or so email newsletters. All the others are fine. Once the script busy notification occurs I have to end the Firefox process(es) in Task Manager.

Thanks

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Hello again, Now, I've got a hypothesis to this problem. Most of the sites that cause problems are tech news sites full of video and ads. They are generally very slow loading. Some can take more than a minute sometimes. When I read an interesting title many times I will use "send link" to send a copy to myself. Many times I get impatient and click once or twice on "send link" before the page is fully loaded. Many times this will work, but occasionally I get the script error. I've been avoiding that impatience and the occurrence of the script problem has been reduced dramatically. I don't know if it is feasible, but Mozilla may want to try to deactivating the "send link" choice while a page is loading! Additionally, other than that now, I don't know which program, Firefox or Thunderbird, is at the root of the script problem.

Thanks

Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a good ad / pop-up blocker.