protojunk said

how can i remove the show history button/arrow on the adressbar?

Are you referring to the forward and back arrow? If yes, you can add the following code snippet to your userChrome.css:

#back-button, #forward-button { display: none; }

Note: Keep in mind that userChrome.css isn't officially supported and that it can break when you update to a newer Firefox version.

I think it's this one:

<xul:image anonid="historydropmarker" class="urlbar-history-dropmarker urlbar-icon chromeclass-toolbar-additional" tooltiptext="Show history"/>

You could try:

#urlbar .urlbar-history-dropmarker {
  display: none !important;
}

By the way, what is your rule for the Page Actions menu button? It seems to have left a large gap. If you are using visibility: hidden that doesn't collapse the space an element occupies. You can instead use visibility: collapse or display: none to recover that space.