For what items does it shows this message?

If a website uses cookies then you should see this when you expand this section. When no such data is stored then usually all sections are collapsed.

• https://developer.mozilla.org/en/Tools/Storage_Inspector

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

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

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

Thanks for your response.

The message shows for every item that I attempt to view.

Neither safe mode/disabling add ons, nor the theme seem to make any difference.

Thanks again. Any support is much appreciated.

Moreover, to clarify, cookies are visible as expected. It is session storage that is prompting the "not data present..."

It seems strange, because I used this feature quite successfully for exactly the same pages in the past.

Are you possibly using Private Browsing mode?

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

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

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