https://support.mozilla.org/en-US/kb/update-firefox-latest-version?cache=no Did you update Firefox to the latest version?

Version 90.0.2, first offered to Release channel users on July 22, 2021

I'm using firefox on linux ubuntu and latest version for me is 90.0 as of now. The version you mentioned is not uploaded to ubuntu repository yet, I think.

How's the proxy configured in the Network settings? Try to switch to No proxy.

set proxy access to no proxy, but didn't help

Try the Firefox version from the official Mozilla server: https://www.mozilla.org/en-US/firefox/all/

now installed version 90.0.2, but result is the same. Firefox can't open certain the mentioned sites. At the same time, replying this text with Firefox browser. Very strange issue.

Make sure you are not blocking content.

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

Troubleshoot mode didn't solve my problem, also deleting caches and cookies. I tried this before, even uninstalled Firefox and all of its data and reinstalled, but the problem persisted. It seems like a network problem, but how other browsers work if there is a network failure. I tested in chromium and brave web browsers at the same time with Firefox. Only Firefox has problematic behavior.

I called for more help.

@FredMcD any update? problem still persists for me... It's strange that I installed Firefox Developer Edition (version 91.0b7 (64-bit)) and confronted with the same problem.

I called for more help. That's all I can do.

You can do a DNS Lookup test via the tool on the about:networking page.

@cor-el can you elaborate? I didn't understand what should I do

Can you check to see if you are blocking any cookies? see screenshot

"Blocked" and "Third party cookies" are totally missing for me. So, I think it means that nothing is blocked.

@cor-el can you elaborate? I didn't understand what should I do

After the last update to version 90.0, I can't continue to use firefox browser. The problem is about opening google sites (youtube, gmail). Other websites seems to work normal, but I can't open youtube and gmail now (google.com itself works heavily). When I type url and click enter, it takes so much time to load, often not loading the site or partially load. Other browsers installed on the same system works normally with the "problematic" websites. I tried hard reload (ctrl+f5), cleaning all browser data, and uninstalling and reinstalling. None of the mentioned actions helped. Please help me to identify and solve the issue.

Can you use OBS to create a video so that we can see what's going on in the section of the screenshot? This section should show what's taking so long to load.

@jonzn4SUSE You can find screencast here: https://www.dropbox.com/s/qbig2srn6lj6vjb/screencast.mp4?dl=0

Thanks for the video, there is nothing that stands out. Have you tried under a different user account?

I didn't try with different user account, but incognito mode has the same unresponsive behavior.