Any add-ons that may still be installed on Firefox that are running ?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

https://support.mozilla.org/en-US/kb/websites-look-wrong-or-appear-differently

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

Them problem also happen in safe mode.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Seems to only happen with google websites (google.com, google translate, ...).

I did previously erased all cache and cookies.

So why only google ?

Also youtube, but that's google too.

So what's wrong with my google ?

FredMcD said

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

I just did that.

No problem after opening hundreds of google search, searching in link bar, search bar, and in google.

I then reboot in normal mode, and I cannot get the problem yet... hoping never.

In safe mode, there's no wifi.

I needed to plug the modem directly to computer.

Now I'm on wifi again. I'll see if problem occurs.

Problem again.

Currently loading gmail to see my mail. It took 20 seconds. Why ?

Then open new tab for google : another 20 seconds. This is crazy.

What's going on with my google ?

I repeat that this problem is ONLY on firefox.

Everything is fine on chrome and ie. But I prefer firefox by far.

I called for more help. Is the problem back with the computer in Safe Mode?

In safe mode, there's no wifi adapter. It works.

I have the problem only on firefox, with my wifi,

When it happens, I have to wait. I cannot open another tab, or refresh. I have to wait. When the page finally loads, I can then open the page multiple times without the problem. A minute later, the problem happens again, I have to wait again.

Disabling router ipv6 do NOT help. BUT I don't have the problem by disabling ipv6 in firefox (about:config , set "network.dns.disableIPv6" to true).

I also have problems on my wifi phone using GOOGLE translate. But I cannot disable ipv6 there.

I don't think it's a router issue. I have a Linksys E1200, latest frameware, and I did resetted the factory defaults.

One day after, still no problem with the "network.dns.disableIPv6" set to true.

So, where the issue ?!? I want to use firefox with ipv6!

WIth ipv6 re-enabled on firefox, on a different wifi, I have no problem.

I think that my Linksys E1200 router is too old (2011) to handle ipv6 correctly. Possible ?

That's not my area. That was very good work. Well done. Please flag your last post as Solved Problem so others will know.