An addon uBlock Origin enables you to right-click an 'element' and block it. https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/

Another addon enables you to make it go away but that's only temporary. https://addons.mozilla.org/en-US/firefox/addon/nuke-anything-enhanced/

Hello, thanks so much for your reply. I'd had ublock installed and tried to block the slider, but it didnt do the trick. Yeah, nuke, as you said, is only temporary. But thanks !

Maybe there is someone out there who comes up with a more permanent solution.

You usually get such a message if a website detects that you want to leave.

The screenshot show that you have clicked the "Log in" button, but that only makes the login form slide in for me.

When does this happen to you ?

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings).

"Remove the Cookies" for websites that cause problems:

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Settings -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or userChrome.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

You might try an e-mail browser such as;

https://www.mozilla.org/en-US/thunderbird/ Thunderbird is a free email application that’s easy to set up and customize - and it’s loaded with great features!

Thunderbird Support Forum https://support.mozilla.org/en-US/questions/thunderbird

New question link: https://support.mozilla.org/en-US/questions/new/thunderbird/form

Thanks for your sugestions. It happens to me when I first browse to the page www.mail.com; not when I leave the page. I do delete cache/cookies from time to time. Mail.com just refreshed their look, and they thought it was a good idea to program this slider.

Thanks for mail provider suggestions. I've got a personalized email address; with mail.com you can choose the ending after "@", so not too eager to change. Maybe I've just got to live with it :/.

Thanks

You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be cautious. If you have a password or other data for that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data for that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox