If you can't find an official installer in the future, please ask for the link. I'll message you.

I notice in the other thread, Firefox 27 started working for no apparent reason. Perhaps some security software was blocking it until it received the all clear???

Thanks for replying so rapidly. Actually, I have turned off Kaspersky AV during one of the installations, following a recommendation I have found online, but to no avail. Kaspersky FF files are old and worked fine until now, so i don't think that's the source of the problem. I managed to operate the FF error console though, and there were some errors, one of them fatal. Unfortunately I didn't made a record of that. Any need of that? I'll try to reproduce if necessary. I'll greatly appreciate if you message me the official v26 he locale. Cheers.

js console errors: 1) Could not read chrome manifest 'file:///C:/Program%20Files/Mozilla%20Firefox/chrome.manifest'.

2)Could not read chrome manifest 'file:///p:/DXoUqot%20TbKHt/ivvSvOj%20mnbtWcn/chrome.manifest'.

3)חותמת זמן: 07/02/2014 02:36:54 אזהרה: WARN addons.xpi: Ignoring missing add-on in C:\Documents and Settings\All Users\Application Data\Real\RealPlayer\BrowserRecordPlugin\Firefox\Ext קובץ מקור: resource://gre/modules/XPIProvider.jsm שורה: 7164

4)חותמת זמן: 07/02/2014 02:36:54 אזהרה: WARN addons.xpi: Ignoring missing add-on in C:\Documents and Settings\All Users\Application Data\Real\RealPlayer\BrowserRecordPlugin\Firefox\Ext קובץ מקור: resource://gre/modules/XPIProvider.jsm שורה: 7164 (twice originally)

5)While creating services from category 'profile-after-change', could not create service for entry 'Disk Space Watcher Service', contract ID '@mozilla.org/toolkit/disk-space-watcher;1'

6)חותמת זמן: 07/02/2014 02:36:54 שגיאה: [Exception... "Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIFile.create]" nsresult: "0x80520012 (NS_ERROR_FILE_NOT_FOUND)" location: "JS frame :: resource://gre/modules/FileUtils.jsm :: FileUtils_getDir :: line 70" data: no] קובץ מקור: resource://gre/components/nsUpdateServiceStub.js שורה: 162

7)No chrome package registered for chrome://branding/locale/brand.properties

8) Direct3D 9 DeviceManager Initialized Successfully. Driver: nv4_disp.dll Description: NVIDIA GeForce 9600 GT Version: 6.14.13.1407

9)No chrome package registered for chrome://branding/locale/brand.dtd

Does #2 seem strange to you, the path on a P drive with such a peculiar folder name? Or maybe it's just a problem converting between character sets that isn't significant. Not sure.

I don't know whether you tried creating a new profile when you had Firefox 27 installed, but for future reference:

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should have completely fresh settings databases and a fresh cache folder.

Exit Firefox and start up in the Profile Manager using Start > search box (or Run):

firefox.exe -P

Any time you want to switch profiles, exit Firefox and return to this dialog.

You'll click the Create Profile button. I recommend using the default location suggested (don't click the button to choose a different folder). Then start Firefox in the new profile you created.

Does it run?

When returning to the Profile Manager, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.

Some of the code says that add-ons are missing. Several things you can try.

Start Firefox in Safe Mode

Go to Mozilla.org and get the full installer.

Open your firewall program. First check the settings. Make sure that the program is set to tell you if a new program wants access to the web. Then go to the list of programs the firewall has. Make sure that all the programs you want to access the web are set to ALLOW. If it is set to AUTO, the firewall may not allow access.

LAST RESORT ! ! Reset Firefox

Thanks for comments!

As a matter of fact, being desperate after several hrs of trying everything, I completely removed all the profiles - so nothing to reset or change - it is all new.

I have tried everything - full installer, stub - of several locales - nothing worked.

Checked my Firewall settings now - all are set to Allow.

As for safemode - FF won't start at safemode. Won't start Profile Manager. Won't start.

The 2nd warning indeed seems odd. Maybe something to do with other device on the network...

checked js console errors in running FF26 - No. 1 3 4 5 8 - appearing there too.

So that narrows down the cause to the other errors.

You said that Kaspersky FF files are old and worked fine. When is the last time you updated Kaspersky? Have you scanned for malware? Use several of the programs listed below.

======================================

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• TDSSKiller - AntiRootkit Utility
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

Well, I have spent all afternoon scanning for malwares, although I have cleaned my machine as part of my initial efforts to make FF27 work using CCleaner.

After removing all kinds of stuff and reboot, I reinstalled FF27 and now it works...

I have used MalwareBytes' Anti-Malware (I think this one did the trick), Hitman Pro and ad-aware.

When scanning for malware, you need to run several of the malware scanners. Each works differently. If one program misses something, another may pick it up. Happy Computing.