The latest Chrome update Version 45.0.2454.93 m as fixed this problem. Haven't checked the latest Opera & don't intend to ! Spent enough time trying to find a solution. Two browsers now work..Chrome's latest and IE V11.

An update to my last & for anyone following this conversation..

I had to run the diag Deployment Image Servicing and Management (DISM) to correct an M$ stuff up which caused the System File Checker (SFC) to fail with multiple file errors. After DISM corrected the Win Update problems with SFC, it ran OK with no file errors reported.

Thanks blackbird71 for the very helpful suggestions.
It's going to be a time consuming process, but since I have no choice & the Chromium forum has been no help, I have no choice. Since IE V11 is now running ok & Firefox is a pain to use, I'll uninstall the later, & debug running Opera, or Chrome & uninstall the Extensions as you have suggestion.

I have to virtually restart the debug process all over again. It's been so long since I last did it ! especially now IE V11 runs OK ?

I will report the outcome, after I've repeated the Extension checks. Thanks again

@blackbird71, Didn't see your last post until I'd just sent mine. I had to leave the screen.

I've stopped using Firefox. The setup is a maze of options. It's confusing & my last attempt to use it was causing me angst ! I just want a browser that works without jumping thru so many hoops & problems.

I'm going to try Chrome's latest which I haven't yet installed.

Just noticed I said ADPlus in my previous post which is the Ad Block Plus extension. It's not blocking any ads in the forum.
Privacy Badge has found another tracking cookie (total 7). Six are unblocked & it's blocking stats.g.doubleclick.net. I'm glad it is. Another nosy Google tracker. The forum is still running AOK with no JS errors.

Thanks for reminding me. Might have been a slip of the tongue (so to speak). I do remember using IE after Chrome & Opera failed & it also failed. It has now Auto updated to IE V11 & runs AOK.

Just checked ADPlus.It's not blocking any ads. Privacy Badger has indicated 6 suspicious tracking cookies, but I haven't allowed it to block any. Normally I'd block all of them because it's my PC & I'll decide what does or does not run..

I'll redo the chrome browser debugging, to see if anything has changed with the latest chrome update. Maybe it works now.
I know the last Opera updates were a problem. I tried them & reverted to the last V29 version. I prefer Opera which is why I'm trying to resolve the JS bug, so I can let it update..

Thanks joshi, I'd totally forgotten Ff uses the Gecko engine.

Therefore, since Mozilla (Gecko) & Google (Chromium) are probably not swapping code, it immediately reinforces the probability, it is an extension. I had previously shut them all down & reloaded one by one, but was unable to pin point any one of them as the problem. I'll re-install & redo each extension isolation tests again.

@sgunhouse Thanks for the suggestions. Appreciated. I covered some items with blackbird71.

I use WIN 8.1 with M$ stock standard Windows firewall & Windows defender which is updated a couple of times/day. If I knew which Extension was a cause I'd disable it in a flash (no pun intended).

The most likely suspects would be Ad Block Plus which tells me it's not blocking any ads on this forum or Privacy Badger which isn't blocking any tracking cookies on the forum site. I don't have a problem with the forum.

I have disabled both when trying to run with a later version of Opera/Ff or Chrome. That didn't solve the JS problem. I'm guessing but it looks to me like a Chromium problem, which fails in all three of the browsers I've tried, with the JS script error. Excluding Opera V29.0.1795.60 which I'm using at present & doesn't suffer the JS error problem.. I'm clutching at straws !

@blackbird71
Thanks for your comments & observations. Appreciated.
I don't recall including IE in my previous messages. IE doesn't seem to suffer from this error. It may but since I dislike IE, I rarely use it.

However, I believe Chrome, Opera and Firefox all use, or base most of their code on Chromium source code. Maybe most of it, I've no way of knowing. I've tried all three. The JS problem occurred on & after Opera V30. All later Chrome & Firefox as they were updated, also failed with the same error message.
I'm not exactly sure what it's complaining about. (more about this in my next para).
The error message I posted in my original post was..

"Javascript is disabled in your web browser. If you enable JavaScript, this text will change"

As I've stated previously,.. JS is enabled in my browsers. I never turn it off.

I'm still running Opera 29.0.1795.60 which doesn't suffer this problem. I've also used the same Extensions with each browser update. The problem (error) is I believe an IFrame problem. I do recall (it's been so long since the problem first occurred, it's a bit hazy but), my debug efforts suggested IFrame blocking was the cause due to some security concern within the Chromium community. I don't know if the Opera forum (this site) uses IFrames. The forum site runs OK, so I'm assuming it doesn't ?

I've installed every release of all three browsers, since Opera V29.0.1795.60, using the same Extensions, & the problem persistently occurs in all three. Having spent so much time trying to correct this problem, I've resigned myself to staying on Opera V29. It's not my preferred choice.

Does that mean...NO Speed Dial Sync from user/1 to user/2 or Guest etc when the Extension is installed on each?
I run Admin (supa user) & NON Admin users with my browser.
Opera wont sync my NON admin user dials to my Admin user.
It's tedious copying ALL of them from one user to another !

Just noticed..Opera has integrated Speed Dial with the browser. It's not a separate extension. So we are dependant on Opera for an upgrade !

Does that mean...NO Speed Dial Sync from user/1 to user/2 or Guest etc when the Extension is installed on each?

I run Admin (supa user) & NON Admin users with my browser.
Opera wont sync my NON admin user dials to my Admin user.
It's tedious copying ALL of them from one user to another !