Hello JqPublic, try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

thank you

Can you use the cursor keys?

You can use "Ctrl+Shift+Page Up" and "Ctrl+Shift+Page Down" to move the current tab left or right.

You can press Ctrl+L (Mac: Cmd+L) to set focus to the location bar and press Shift+Tab if the tabs are on top or the Tab key if the tabs are on bottom until the tab bar gets focus and shows a focus ring.

If the Tab bar has focus then you can use cursor Left and Right keys to go to the next or previous tab or use Ctrl (Mac: Command) and cursor key to move tabs.

• Ctrl+Left moves the tab one position to the left
• Ctrl+Right moves the tab one position to the right
• Ctrl+Home moves the Tab to the far left (first tab)
• Ctrl+End moves the Tab to the far right (last tab)

Probably reason:

SM_CXDRAG and SM_CYDRAG (WINAPI, GetSystemMetrics) equal 0 is interpreted as infinity.

The bug was detected and filed with ID: bugzilla.mozilla.org/show_bug.cgi?id=1195035

How try to fix it:

1) Run Regedit.exe 2) In the left panel click: HKEY_CURRENT_USER, Control Panel, Desktop. 3) in the right panel double click: DragHeight and type 4 (it's default value) 4) in the right panel double click: DragWidth and type 4.

Close Regedit and restart your computer.