First: Customize Firefox controls, buttons and toolbars {web link}

Type about:customizing<enter> in the address bar.

Note: about:customizing is no longer present in Firefox 47+ releases.

• Press Alt or F10 to bring up the Menu Bar.
  Then View > Toolbars > Customize.
• Right-click on a blank spot in the toolbar and
  select Customize.

In the new window, look for the icon. When you find it, hold down the left button on it, and move it to where you want it to be. You can move any of the icons you want from here, but; some icons are locked in place.

There is also a Restore Defaults button at the bottom middle.

After: It’s possible that there is a problem with the file(s) that store the extensions registry.

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Delete all extensions* files and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

After, restart Firefox.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions

• https://support.mozilla.org/kb/Unable+to+install+add-ons

+++++++++++++++++++++++++++ You will have to approve the updating one last time.

Thank you for your detailed answer, i did already check the customize setting but the icon of adblock is not present sadly, i did reinstall again my firefox (even though it was a clear installation to begin with as i got my pc fixed some days ago) and i did manage to get addblock and another addon to show up in the top right bar and work, but after i turned on the pc again the day after it was back where i started. I redid another clean installation of firefox but still having this issue, do you think addblock is not supported anymore? Not sure what could cause this weird behaviour

Did you check out my second post?

Yes ofcourse, but it didn't quite work out sadly

Did you try Restore Defaults in Customize mode ?

• https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

Yes i tried this as well but no luck so far

Try to uninstall adblock and close and restart Firefox and reinstall the extension or possibly try another ad-blocker.

• https://addons.mozilla.org/firefox/addon/ublock-origin/

I tried but same result as adblock, the addon doesn't display the icon on the top right and i still see adds like it's not working

I'll rebump to say that now firefox somehow manage to disinstall my plugin, i reinstalled a plugin yesterday to see if i would be able to fix the issue, and now the plugin is not found at all (still having the problem mentioned at the start)

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Thank you very much for your help Fred and Cor-el. I noticed that if you do put in the option of firefox never remember history, this might be the cause of what might not let the addon work at all and be displayed in the top right bar, as silly at it may sounds, i'll do a quick restart to be sure of it, i'll edit this message if possible

Edit, indeed it was that option of firefox that caused the problem it seems

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems.