Is it the yellow bar saying a script is slowing down the tab? If not, what does it look like, I can't recall ever seeing one that mentioned an extension.

Hello,

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Thank you!

It's happened again. I was going to give a screenshot anyway when it did.

Start to load the web page. But STOP the page loading. After the page is loaded, click the AdBlock icon. Now select Disable on <website>. After, reload the page.

Why should I have to disable AdBlock on YouTube because of Firefox? I want to disable the message which is completely unnecessary.

I take it there's no way of disabling this message which came up yet again after I opened a new YouTube tab for all of one minute? It's getting ludicrous.

Your screenshot mentions the uBlock Origin extension. There is a community support site for uBlock Origin on Reddit where you can ask about that dialog and get suggestions:

https://www.reddit.com/r/uBlockOrigin/

Again the problem isn't uBlock Origin or Adblock Plus. It is Firefox not allowing me to disable this message which actually points me to an issue which isn't a problem for me. What it does is on occasions when I'm watching a YouTube video in one tab switch to another tab and show this unnecessary message which it looks like can't be disabled. I'm sorry but Firefox has become increasingly poor over the last few years. I've been a user of Firefox since it started and of Netscape before that but it's becoming worse and worse.

What the screenshot shows is the uBlock scrip is taking too long to run and the browser thinks it is stuck. See if this helps.

”Webpage is slowing down your browser” This is the new way the browser tells you there is a problem with the script program(s). https://support.mozilla.org/en-US/kb/warning-unresponsive-script?cache=no

https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox

... ..

As I wrote earlier changing dom.max_script_run_time does nothing to extend the time. Blocking scripts doesn't seem to stop it either although again the issue is Firefox demanding I know something I'm not that bothered about. It's making opening multiple an issue which is ridiculous.

Is this with all websites/pages, some, a few?

Disable the AdBlock add-on.

This whole exchange shows where Firefox is going wrong.