I'm not sure if the following will solve your issue but I've been recommended buy Kaspersky support to uninstall the previous version and install the new one.

Said that, I do recommend first to clean up all your browsers cache because I don't have any problem with C3 with the new Kaspersky.

If still the problem occur please try to uninstall the antivirus and be sure to remove Kaspersky configuration while uninstalling and install it again from scratch.

If doesn't work please open a ticket with Kaspersky support.

Cleared the cache and it worked. Not sure if it's because of that or firefox just got it's stuff together, but thanks man. :]

Hey there, so I'm using Kaspersky and trying to get into Construct 3 and have run into similar problems. First, however, thanks to the moderation team and rraffo for putting effort into trying to solve this issue. I was expecting to have to do some deep forum digging and it was a welcome surprise to find a whole guide on how to solve the issue.

I am currently using Kaspersky version 21.1.15.500 (2021 issue) on Mozilla Firefox. First and foremost, with this version, I am still experiencing the Issues Loading Construct error. When disabling "Inject script into web traffic to interact with web pages" under the networks tab, I no longer get the error message, however, am met with a grey loading screen and a message at the bottom that says "waiting for ff.kis.v2.scr.kaspersky-labs.com..." I believe it's stuck there. The firefox addon for kaspersky also doesn't do anything to fix this issue.

On the other hand, adding Kaspersky to the network exclusions and running it on incognito mode does fix this issue, however, incognito mode is pretty inconvinient if I want to use this program often. Curiously, Construct 3 still works on Google Chrome and Opera, just conviniently not Firefox. Once again, this is more of an inconvinience for me since I use Firefox for personal stuff and don't use the other browsers often.

Here is the console log for Firefox (not working):

Content Security Policy: The page’s settings blocked the loading of a resource at inline (“script-src”).

That's it.

Here's the console log for Google Chrome (working):

Registered root service worker on https://editor.construct.net/ root-sw.js:273 [Root-SW-Offline] Up to date main.js:252 Error while parsing the 'sandbox' attribute: 'allow-storage-access-by-user-activation' is an invalid sandbox flag. d.pLb main.js:252 main.js:2004 Stop! main.js:2004 This is a browser feature intended for developers. If someone told you to copy and paste something here to enable a feature or "hack" something, it is a scam and may allow them to steal your account information or your work. main.js:2004 Note: this is the developer tools console for the Construct editor. If you're looking for developer tools for preview, be sure to open developer tools for the preview window instead. 3main.js:2080 [Analytics] Sandbox iframe unavailable, skipped logging BIa main.js:2080 main.js:2013 Registered service worker on https://editor.construct.net/r210-2/ 6main.js:2080 [Analytics] Sandbox iframe unavailable, skipped logging BIa main.js:2080 main.js:2080 [Analytics] Sandbox iframe unavailable, skipped logging BIa main.js:2080 Mfa main.js:2078 E main.js:2009 Y2c main.js:2011 requestIdleCallback (async) kd main.js:436 (anonymous) main.js:437 d.Jk main.js:437 AVb main.js:2021 async function (async) AVb main.js:2021 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 main.js:2080 [Analytics] Sandbox iframe unavailable, skipped logging BIa main.js:2080 Mfa main.js:2078 E main.js:2009 Y2c main.js:2011 async function (async) Y2c main.js:2011 requestIdleCallback (async) kd main.js:436 (anonymous) main.js:437 d.Jk main.js:437 AVb main.js:2021 async function (async) AVb main.js:2021 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 main.js:2080 [Analytics] Sandbox iframe unavailable, skipped logging BIa main.js:2080 Mfa main.js:2078 Y2c main.js:2011 async function (async) Y2c main.js:2011 requestIdleCallback (async) kd main.js:436 (anonymous) main.js:437 d.Jk main.js:437 AVb main.js:2021 async function (async) AVb main.js:2021 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436 requestIdleCallback (async) kd main.js:436 md main.js:436

I don't know if it's significant, but I had the old version of Kaspersky (2020) and didn't uninstall it before installing the new one, but I'm pretty sure that isn't causing the issue. With the old version of kaspersky, disabling "Inject script into web traffic to interact with web pages" didn't work either.