If the screen is flashing, there may be some incompatibility between Firefox and your graphics/display software.

Could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the option/alt key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

There is a risk of losing history, saved passwords, and some other data when installing an older version of Firefox and using your same settings. See: Install an older version of Firefox.

There is a separate board for Thunderbird support, so it's best to post a separate question about that:

https://support.mozilla.org/questions/new/thunderbird/fix-problems

jscher2000 said

If the screen is flashing, there may be some incompatibility between Firefox and your graphics/display software. Could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem. If Firefox is not running: Hold down the option/alt key when starting Firefox. If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart. Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh). Any improvement?

---

There is a risk of losing history, saved passwords, and some other data when installing an older version of Firefox and using your same settings. See: Install an older version of Firefox.

Thank you for all the above information. Starting in Safe Mode helped me access my webmail (so far). What now? How do I know what Add Ons and Extensions were disabled please?

jscher2000 said

There is a separate board for Thunderbird support, so it's best to post a separate question about that: https://support.mozilla.org/questions/new/thunderbird/fix-problems

Thank you. I appreciate the information. I have sent the message to T'bird support before but have never received a resolution to the vanishing scroll bar. :( I'll try again.

On Mac the scroll bars can be hidden and only have them show when you scroll the page so you can see the current scroll position. You can make the scroll bars always visible:

• System Preferences > General > Show Scroll Bar > Choose "Always"

cor-el said

On Mac the scroll bars can be hidden and only have them show when you scroll the page so you can see the current scroll position. You can make the scroll bars always visible:

• System Preferences > General > Show Scroll Bar > Choose "Always"

cor-el - THANK YOU! Such an easy fix. I really appreciate the help.

fabprin said

Starting in Safe Mode helped me access my webmail (so far). What now? How do I know what Add Ons and Extensions were disabled please?

Basically, all extensions are disabled in Safe Mode. You can view, disable, and often remove extensions on the Add-ons page. Either:

• Command+Shift+a (Windows: Ctrl+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 you do not remember installing or why? If in doubt, disable (or remove).

Any improvement?

However, regarding the screen flashing, if that turns out not to be caused by extensions, you can disable Firefox from using hardware acceleration, which works around incompatibility with your graphics card/chipset software. See: Firefox's performance settings.