Are we talking about Firefox or Thunderbird?

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies
  Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} A small dialog should appear. Click Start In Safe Mode (not Refresh). While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe websites. Are there any problems?

Then restart.

Thank you for your quick response. I have tried all options as you advised, unfortunately, the message still appears.

I am working in Firefox by the way and it had been much of help of you to know that I have to empty regularly cookies and cache in Firefox itself. It fastens the upstart, that is at least an improvement.

All other websites on Firefox just work in the proper way, it is only Outlook mail where this message continuously appears.

There is a question left: when you say "start-up" do you mean "start-up" only Firefox application or the whole computer?

When you make changes in the options of Firefox, the change is recorded immediately. But a few items require that the browser be restarted.

Thanks for your support, I have noticed it that changes are recorded directly.

A complete shutdown and startup doesnot solve the problem either.

Maybe I should post a problem at "outlook forum" see if it has anything to do with the connection between Firefox and Outlook (cause the problem is only occuring when using Outlook) not any other emailprovider or website running under Mozilla Firefox.

Hope to get the problem solved.

One thing you can try is Windows Live Mail program. Windows Live Mail is part of Windows Live Essentials

Yes that is possible. It is already integrated in my current Windows 7.

Only use might give me another problem and besides that I cant get used of the layout and division of subjects.

If the problem remains I think I have to live with this. Maybe upgrading to Windows 10 is the solution, but I am afraid new problems arise. Better 1 existing problem than 10 new to come. :-)

I ll see what I do, thank you.

I might have found a solution to avoid the appearing message and that is entering the mailbox via url: www.live.com.

As you know Outlook can be entered in different ways using different names like hotmail, outlook and live.

Instead of Outlook I used as a trial several times live.com now and it seems to work.

That was very good work. Well Done. Please flag your last post as Solved Problem so others will know.