Hi lse123,

The first thing to explain is that older versions are not secure and not supported, therefore they increase the risk to your personal data and your computer system. Of course if you are running on a secure intranet, &/or have bare metal backup procedures in place that may not be a concern.

Secondly running multiple versions is probably considered an advanced topic, and not something the standard user would need to do, but it is all relatively easy and simple to do. Just take care, back up bookmarks & settings and be careful what you do with profiles, until you fully understand them.

You may well decide to keep IE (for instance for Windows updates) and then use one of the Firefox versions as a default browser. (will be associated with the .html file types for instance) The -no-remote command line argument is used to start a further instance of Firefox and allow it to run simultaneously. This option is not used for the version chosen as the default browser.

To do this successfully you need separate unique profiles for each Firefox version. Remember bookmarks & settings are contained in these profiles. Take care with profiles, use only empty folders for creating the new profiles (otherwise deleting profiles will destroy other data) and it is probably sensible at least initially not to delete or rename profiles, choose distinctive names (maybe not the version number, that could change if you upgrade - remember he 6 week rapid release cycle.) Presumably you are also aware of the Aurora, Beta & Nightly channels.

You will need to choose the custom install option when installing, or you will just overwrite each install in turn.

For detailed info follow the links from

• backing up your information
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox
• managing profiles
• http://kb.mozillazine.org/Command_line_arguments <--- note -no-remote
• https://addons.mozilla.org/en-US/fire.../language-tools/
• http://www.mozilla.org/en-US/firefox/all.html

"You will need to choose the custom install option when installing, or you will just overwrite each install in turn. "

"custom install option", if choose this you mean i have option keep old version...or is other setting...for this? basically / briefly to keep old and install new in new dir what must do? 1., 2., 3., ...

answer above and this.. if want install an old version, can I? how?

You will have to install the different versions in separate directories (Example, Firefox 6 in program files\Firefox6, Firefox 11 in program files\firefox11 etc.).

If you don't mind me asking, is there a specific reason you want to have the older version of Firefox? It is quite insecure, and as several known issues.

Read the linked articles for instructions on what to do, and add this one to the list:

• http://kb.mozillazine.org/Installing_Firefox_on_Windows#Custom_installation

i am web developer that's why...

well go ahead(first backup) and choose custom install and choose other dir...

only this for two versions, correct?

can I have 3 versions installed? can run same time 2 firefox versions?

You can have as many versions as you want installed on your PC. If you wish to run multiple versions at the same time, just remember to use the no-remote

"no-remote"

this is for running multiple instances same time NOT for install , correct?

This is a command line argument. You may well in fact use it as part of the installation process in that you may for instance wish to create shortcuts to use for startup of the different versions.

• see http://kb.mozillazine.org/Opening_a_new_instance_of_your_Mozilla_application_with_another_profile
  clickable link __^^ -- (blue text)

Are you managing to find and read these linked articles ?

The above for instance includes

Important: Never use -no-remote to start the "default" profile ..... 
You can use a shortcut to a specific profile to open Firefox using -no-remote. For example, .....

English will not be your first language. Have you considered trying Google translate. Google translate will translate blocks of text or whole webpages. The results are not always good but may be useful.

• http://translate.google.com/

Английский не будет вашим родным языком. Рассматривали ли вы пытаться Google Translate. Переводчик Google будет переводить текстовые блоки или целые веб-страницы. Результаты не всегда хорошо, но может быть полезным.

• http://translate.google.com/

this is correct?: "no-remote" no needed if plan install 2 versions as in my case, but use only one same time.

how choose upgrade one of the two versions(the newest ver) if upgrade time comes?

We now have the rapid release system with new versions coming out each 6 weeks.

When my Windows system is working I usually have Firefox 3.6, as that has had continuing support, then the Release, Beta, Aurora & Nightly channels allowing them to update as required. I have no need normally of the unsupported versions 4 to 9, although I do see a case for keeping the two Release channels, and not updating one of them immediately, so at the moment maybe keeping 9 & 10

if have 6.02 and 11.0 can/how upgrade 11.0 only?

If you have Firefox 11 open and installed in a different directory, just upgrade from inside Firefox 11 sing the internal updater. Updating Firefox

I installed in differ dir the 11 but layout seems the same, when start-up Firefox from windows explorer C:\Program Files (x86)\Mozilla Firefox // 6.0.2

C:\Program Files (x86)\Mozilla Firefox 11

this the last choice I am doing of the two, become the default when start-up with other ways clicking icons:desktop, Quick Lunch, Programs... well where is error?

eg windows explorer start-up 11 other ways 11 all...