On https://simple-vt-demos.jakearchibald.com/bounce/ , with DevTools opened, if I reload the page, I'm getting an exception from https://searchfox.org/firefox-main/rev/a5316cedc669bcec09efae23521e0af6b9d3d257/devtools/server/actors/string.js#36

initial: this.str.substring(0, DevToolsServer.LONG_STRING_INITIAL_LENGTH),

exception: this.str.substring is not a function
this is because this.str is a Promise, not a string

The stacktrace points to https://searchfox.org/firefox-main/rev/a5316cedc669bcec09efae23521e0af6b9d3d257/devtools/server/actors/network-monitor/network-event-actor.js#661-667,674

/**
 * Add network response content.
 *
 * @param object content
 *        The response content.
 */
addResponseContent(content) {
...
  content.text = new LongStringActor(this.conn, content.text);

Here, content.text is a Promise
it's build from https://searchfox.org/firefox-main/rev/a5316cedc669bcec09efae23521e0af6b9d3d257/devtools/shared/network-observer/NetworkResponseListener.sys.mjs#564-567,630,633

/**
 * Create the response object and send it to the client.
 */
#getResponseContent(data) {
...
    response.text = text;
...
  this.#httpActivity.owner.addResponseContent(response);

where data is the Promise
it comes from https://searchfox.org/firefox-main/rev/a5316cedc669bcec09efae23521e0af6b9d3d257/devtools/shared/network-observer/NetworkResponseListener.sys.mjs#346,375-377

onStartRequest(request) {
...
  if (isOptimizedContent) {
    const data = this.#getContentFromCache();
    this.#getResponseContent(data);

and indeed #getContentFromCache is async https://searchfox.org/firefox-main/rev/a5316cedc669bcec09efae23521e0af6b9d3d257/devtools/shared/network-observer/NetworkResponseListener.sys.mjs#656

async #getContentFromCache() {

Bomsy, it looks like this might have come from Bug 1830230, can you check?

Thanks Nicholas,
Yes indeed this was likely introduced by the refactoring i did in Bug 1830230.

I was not able to reproduce on the page provided , but was able to reproduce by just refreshing on https://nchevobbe.github.io/demo/console-test-app.html

Set release status flags based on info from the regressing bug 1830230

https://hg.mozilla.org/mozilla-central/rev/0b4cfff1ae81

The patch landed in nightly and beta is affected.
:bomsy, is this bug important enough to require an uplift?

• If yes, please nominate the patch for beta approval.
  • See https://wiki.mozilla.org/Release_Management/Requesting_an_Uplift for documentation on how to request an uplift.
• If no, please set status-firefox145 to wontfix.

For more information, please visit BugBot documentation.

firefox-beta Uplift Approval Request

• User impact if declined: Will impact users ability to copy all or save all requests as har
• Code covered by automated testing: yes
• Fix verified in Nightly: yes
• Needs manual QE test: no
• Steps to reproduce for manual QE testing:
• Risk associated with taking this patch: low
• Explanation of risk level: Small js fix
• String changes made/needed: none
• Is Android affected?: no

Original Revision: https://phabricator.services.mozilla.com/D270083

(if this gets uplifted to release, we should take Bug 1991020 as well to avoid frequent test failures)