Please check if all your plugins are up-to-date. To do this, go to the Plugin Check site.

Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow Update button or a red Update now button, please update these immediately.

To do so, please click each yellow or red button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.

The computer asked you for your password? Or Firefox?

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Once you've done this, attach the saved screenshot file to your forum post by clicking the Browse... button below the Post your reply box. This will help us to visualize the problem.

Thank you!

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

Dear Fred McD,

Thank you for your reply. In response, I do not get asked for a password, or for Firefox. It is just that when I start my computer, I get the following message, and I attach a screenshot of the message. After that, though, Firefox seems to run slowly. When I try to load a website, it seems to take a fairly long time. The circle in the middle of the tab seems to rotate a long time, before the site is loaded. Marek

Nice bluebird. Did you press yes or no?

You said you get this when the computer is booting up? That address in the box is a web address.

Troubleshoot Firefox issues caused by malware article.