What's your computer system and Firefox version?

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

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Hi Fred,

When in safe mode it works just fine

Windows 10 firefox version 63.0.3 (64-bit)

Hi evinp, if you can load tabs successfully in Firefox's Safe Mode but not in regular mode, check whether one of your extensions might be the culprit.

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything tab-related, or that could block content, or that you just do not remember installing or why? If in doubt, disable (or remove).

Then test again. Can you fix it by disabling one or more add-ons?