Multiprocess compatible? Rated 5 out of 5 stars

It's still a great and useful extension.
Especially the activation just for certain domains and the integration into the sourcecode window are nice.
But I am afraid the addon will stop working soon, when e10 (multiprocess) support will be required.

Answer to your reply:
I have e10 disabled anyway so far. But the mozilla compatibility reporter says html validator doesn't work with multiprocess. I also checked that in a new profile (see screenshot) where e10 actually was enabled.
So it may be just a problem with the automatic compability recognition or formalities in the manifest.

Also see for further links/info.

More info please !!

E10 is normally implemented in the extension. At least the part of chrome and content. Webextension is not. It is a huge task.
E10 is a complex and it is very possible that I missed something.


Fatal error with 64-bit version Rated 5 out of 5 stars

Good extension.

I habe 64-bit firefox also installed but i got a error in the 64-bit version:

The dynamic C library contained in the extension file could not be found

Hope this could be solved.
In 32-bit version FF everything ok.

Firebug et HTML Validator Rated 3 out of 5 stars

J'ai un problème de conflit entre firebug et html validator avec les dernières versions.
Lorsque html validator est actif, l'affichage de firebug est modifié et certaines fonctionnalités ne sont plus disponibles ?

Merci pour le feedback

Pourriez-vous m'envoyer par mail,, un screenshot du probleme, les versions de Firefox, HTML Validator, Firebug et le type d'Operating System ? Merci

Usefull, but requires more help messages Rated 4 out of 5 stars

Some errors are a bit missleading when localized. Requires more help messages for errors. Or at least show english help if localized is missing.

Please mail me

Please be more explicit, I think that there are 400 errors message descriptions. The extension is translated in 14 languages, and only 2/3 for the full errors.

Still doesn't work with CSE HTML Validator Rated 2 out of 5 stars

Sadly this still doesn't work properly with CSE HTML Validator.

This user has a previous review of this add-on.


Thanks for the feedback. I do not have CSE validator on my machine anymore. I mail Albert W, the owner of CSE to try what we can do to help you :-) beta works with trunk SeaMonkey on Linux64 Rated 5 out of 5 stars

I've been testing HTML Validator Beta with no problems on the version of SeaMonkey mentioned below, comparing "Tidy" results with "SGML" results. In particular the "Tidy" version found attribute errors (including quite a number of mismatches due to typos between the name= and id= attributes of <a> tags). :-)

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0 SeaMonkey/2.47a1
Build identifier: 20160625075045

Great that it has ceased being "Windows-only".

P.S. One unclosed <a> tag caused several "anchor already defined" warnings, but once I had noticed and fixed the error the spurious messages disappeared.

Wrap Long Lines not works Rated 4 out of 5 stars

When I open source code in new window then "Wrap Long Lines" option in View menu doesn't work correctly. When I switching to viewing source code in Tab then all works fine. Please fix this.

This review is for a previous version of the add-on ( 

Thanks! Rated 5 out of 5 stars

I just wanted to express my gratitude to Marc for keeping this add-on alive and updated since so many years. It's an indispensable tool that I use every day.

This review is for a previous version of the add-on (  This user has a previous review of this add-on.

Source code disappeared Rated 5 out of 5 stars

Hello Marc, we daily use the HTML validator extension. We are happy that it already can validate HTML5 code locally. However since couple days we are experiencing problems. If we press Ctrl+U, nothing will show up, only a white screen. If we want to see the source code at least, we must uninstall the addon first. Are you aware of this trouble? Thanks for help!

This review is for a previous version of the add-on ( 

Please mail me

Hi Misinko,

No, unhappily I am not aware of any issue now.

Can you send me a mail ( with
- version of Firefox / HTML Validator that you use
- screenshot of the issue
- OS system and OS version
- The output of the browser console (Developer Tools/browser console)
- When you see the view source, does it pop up in a tab or in a separate window ?


Pretty good Rated 4 out of 5 stars

Make sure to set HtmlTidy as the validation template everyone!
The default one makes no sense.

This review is for a previous version of the add-on ( 

Algorithm choice screen is unreadable! Rated 5 out of 5 stars

After downloading I was presented with a table with options I could barely read - white text against a light blue background. So I dismissed the box and the user guide page was opened in a new browser tab, explaining the options - which I can setup via preferences in the extension window. I haven't got round to using the tool yet - but to be presented with options that weren't readable is off-putting! I'm not sure if this is specific to another extension I have enabled - e.g. no squint. But this was set to show black text against a white background as default. I disabled nosquint - but the html validator colors remained unreadable. So, assuming the colors have nothing to do with my existing extensions (even if they do?) - please could these choices be presented in a more readable way. Note: I don't have an array of extensions installed - nosquint, noscript, and newscrollbars only. So, seems unlikely they are to blame.

This review is for a previous version of the add-on ( 


Thanks for the feedback.
Would it be possible to send by mail more details like OS, version of Firefox, the extension version and if possible screenshots of your issues
It seems that something is broken with new Firefox versions.

My mail is Thanks

Linux64 Rated 5 out of 5 stars

Using Linux64bit Firefox, didn't show up in the "View Page Source" tab, so I changed FF's behavior to open source in a new window (Set "" to "false" in about:config). Works again.

This review is for a previous version of the add-on ( 

Version solved the issues! Rated 5 out of 5 stars

The new version its not only signed yet - it solved the issues with windows x64 systems on Firefox 42. I'm very happy that i can use it again. Thanks Marc!

This review is for a previous version of the add-on (  This user has a previous review of this add-on.

Useless - why advertise tool that does not work Rated 1 out of 5 stars

This tool suffers from developers lack of attention to detail. She (or he) does not care that browsers are updated often or need signing. Her lack of planning causes the addon to be blocked due to improper signing.

All responses from this developer blame Firefox - Never takes ownership of her lack of keeping up with rapid pace of releases.

Wake up! Release the source and let the community help you. You just need to ask for help with your good idea. (and don't tell us about how busy you are - software development is not for people who have time on their hands)

This review is for a previous version of the add-on (  This user has 2 previous reviews of this add-on.

The source is here : You are welcome to contribute :-)
I am currently looking for a way to compile the extension with Firefox on Windows 64 bits. But it is not working. Any help is welcome.


Not working Rated 4 out of 5 stars

The plugin worked great, but now it doesn't work at all. Changing the the algorithm didn't help.
I'm using FF 42.0.

This review is for a previous version of the add-on ( 


Please mail me ( with a screenshot, OS, and explanation of what does not work ? Note, Firefox Windows 64 bits is not supported yet. Please mail me if you use it, it seems that this version that was never used and discouraged is now used by a growing number of people.


Does not work in Firefox Developer 44.0a2 Rated 5 out of 5 stars

Love this tool.
It does not work in the new version for Firefox Developer 44.0a2.
Nothing happens when I click the link. The drop arrow will show the other options, but they do nothing too. Yours is the only tool I can use since I work on a vpn and need a validator that works local on my computer.

This review is for a previous version of the add-on ( 


Hi Steve,

Please read this.

In short, Electrosys is by default in 44a2. Mozilla dev team would like to disable the overlay of XUL... What will make impossible for an extension to modify the screen of Firefox.

Due that most extensions do this, most should be broken. And possibly impossible to redo with Electrosys.

In HTML Validator case, it would be then impossible to change the View Source page with the errors.....

Html Validator for Firefox 64bits on Windows Rated 5 out of 5 stars


Is this addon works with Firefox 64bits on Windows ? I try and the table in the source code window is empty


This review is for a previous version of the add-on ( 

Firefox Windows 64 bits

It has just never been compiled for Windows 64 bits. From what I know (6 month old) Firefox did not wish to have a 64 bits browser on Windows due to incompatibility with most Plugins ?

Where did you found out Firefox 64 bits. Just curious ?
Please respond to


Doesn't work on FF 40 Rated 1 out of 5 stars

If you want to waste about 10 minutes of your time, install this plug-in. Doesn't work.

This review is for a previous version of the add-on ( 

Please mail me

What did happen ? I do not know a case where it does not work. And it works for a lot of people with Firefox 40. I guess that you do not use the normal Firefox ? Please give screenshot and OS/browser version that you use exactly. Thanks.
Please answer to

Linux 64 Bit - I don't understand the answer Rated 2 out of 5 stars

what has a newer version for Windows to do with the missing Linux x86_64? i am using 64bit-only Systems and only Linux for at least 7 years now including that addon *but* for x86_64 you always needed to use the upstream version, no problem so far, but when signed addons get mandatory it becomes a serious problem

This review is for a previous version of the add-on (  This user has 2 previous reviews of this add-on.

Thanks for the headup. It worries me too. My answer was too small. I think it is best if you send me a mail.

In very short, there are several problems. Historically, I uploaded the Linux version here. But I stopped. There are several things that worries me:
1) Most people do not know if they run a 32 or 64 bit version of Firefox on Linux. And there is just Linux option in amo. No way to differentiate 32/64.
2) In the past, it did happen that the auto update did update automatically users of 32 bits with the 64 bit version and the opposite.
3) The time to review is huge. And I need to redo this 4 times. Uploading the extension failed 5/6 time when I submitted 0.962 windows version. I wait that this one is done before to redo it. Knowing that I will get issue because of 2 and 3

So, I have no good solution.
My idea today is to upload the 64 bit version here only ?
Any better idea is welcome.


Ps: I changed the code a little so that :
- the Linux version now contains the 32 and 64 bits library
- and detects the good library automatically.
- After that I have uploaded (08/09/2015) the Linux 32/64 bits and MacOSX on AMO to get signed.

My favorite Rated 5 out of 5 stars

For a long time there was a warning about the particular w3c API being deprecated, and now it no longer works at all.

Edit: dev fixed and made new release very quickly. 5 stars now.

This has been my long time favorite, especially when developing internal websites that the w3c validator cannot read directly. It's light and fast. What more could one want?

This review is for a previous version of the add-on ( 


Thanks for the feedback, I look at it...

(Update) Please use version 0.962 that you can find here: