Should scripts be re-running when going backwards and forwards though history?

[vzjrz]

I don't know if this is a greasemonkey or firefox bug but after the new updates I noticed some unusual behavior from my scripts.
Scripts are running again on pages where they already ran when using the back and forward arrows. I checked with the old versions of gm and firefox and that's not how they used to work. In the old version of firefox I guess pages would completely rerender and therefore when scripts reran they would run on unmodified pages.

// ==UserScript==
// @name        Test
// @namespace     test
// @include       *://en.wikipedia.org/*
// @require       https://code.jquery.com/jquery-3.1.1.min.js
// @description test
// ==/UserScript==
(function () {
  'use strict';

   let tests = $('#test');
  
  // Needed with new updates:
  if (tests.length !== 0) {
    console.log('Previous test div detected');
  }
  
  $('body').append('<div id="test">');
})();

1. Install this script and go to https://en.wikipedia.org/wiki/Main_Page
2. Click on a link to go to a different url
3. Go back
4. Go forward
5. Go back

In gm 3.17 this script would never print Previous test div detected but in gm 4.0 going forwards and back multiple times just keeps adding more and more divs.
Is this an intended change?

[Sxderp]

Not able to reproduce with FF 59.0a1 + Latest master.

[vzjrz]

Man I should really test things out before I write bug reports. I found the bug on another site and tried to write simple case for google.com but checking that out now it doesn't appear to work there. I have updated the steps to reproduce it.

[Sxderp]

Cool. Was able to reproduce. I believe I know a fix. Will submit shortly.

[arantius]

This is probably complicated by fastback, which if it applies then the answer is no, but if it does not then the answer is yes.

[Sxderp]

In response to the comment on the pull (I think it's better to respond here then a commit comment).
I see your point, and it can somewhat be forcibly reproduced. The initial post in this issue had used google as a test subject. And for whatever reason google searches don't work with fastback (thus the original problem never appeared).

With the change performing a back / forward on google does not see the script executed. No div was added to the DOM.

[Sxderp]

I had a thought and just tested with #2635 and it looks like that also solves the forward/backward button issue.

[Strubbl]

At the moment with Firefox 87 the behaviour is like this:

1. visit site x and the GM script gets executed
2. visit site y
3. use FF87's history back button
4. site x is shown again, but the GM script is not executed again and the page looks like it was never executed before