HI, am glad you found a solution to your issue. Since this is Solved could you please Mark Your Answer as the Solution so others can find it. Thank You.

mistaPL said

How to disable sidebar at start up? This is a solution - Refresh Firefox https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings I struggled with it and found a solution.

Solved.

Pkshadow said

HI, am glad you found a solution to your issue. Since this is Solved could you please Mark Your Answer as the Solution so others can find it. Thank You.

I have done so. Thanks