To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

When you did the clean reinstall, did you remove the installation folder as shown in step 3? Note that this process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location. (Win7 right click in the Start Menu > Send to Desktop). If it works in Win10 you can drag from the Start Menu to your Desktop or right click and pin the icon in the Task Bar. Try starting from the Start Menu > Mozilla Firefox. You may need to restart Firefox after enabling some add-ons. If it works in Safe Mode, disable any theme or add-ons you have - Add-ons Manager (Ctrl/Cmd+Shift+A) > Themes/Extensions, then if it's OK, re-enable them one by one until you find the culprit. More - Diagnose Firefox issues using Troubleshoot Mode.

Hi, hold down Shift (Option key on Mac) when you start Firefox to start in Safe Mode.

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