I think it is caused by one of your add-ons. You didn't share your list, so here's how to review those:

Open the Add-ons page using 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. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. 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 suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?

If your Extensions list is blank or is blocked from viewing:

Restart Firefox in its Troubleshoot Mode, which temporarily deactivates extensions to prevent interference. You can restart Firefox in Safe/Troubleshoot Mode using either:

• "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)
• (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)

and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

Then check the Add-ons page again.

To return to normal, simply exit out of Firefox and start it back up normally.

Can you regain control of your bookmarks?

I dont have any extension. Can you tell me another solution??

Did you recent install and remove a SaveFrom.net Helper add-on or program? If not, it might have been bundled with some other software. Please scan your system for malware: Troubleshoot Firefox issues caused by malware.

Meanwhile, in Firefox, could you check whether a "policy" is re-adding the bookmark? To do that, type or paste about:policies in the address bar and press Enter to load that page. Normally, the "Active" panel says "The Enterprise Policies service is inactive." Does yours list any active policies?

I entered the website and it ask me if I wanna put a bookmark in my Firefox and after I added it I wasn't able to remove it because i when I restarted my Firefox it appeared again

Did you download anything from the site? Please check your downloads (Ctrl+J).

You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be cautious. If you have a password or other data for that domain that you do not want to lose, make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website, data for that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox