The shortcut to reload a page would normally be Ctrl+R and not Alt+R.

• https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly
• https://support.mozilla.org/en-US/kb/mouse-shortcuts-perform-common-tasks

Did you make changes to ui.key prefs (ui.key.chromeAccess and ui.key.contentAccess) to use Alt instead of Ctrl?

• http://kb.mozillazine.org/about:config

Ctrl+R causes reload. Alt+R causes READER MODE. After misspushing Alt+R Firefox goes to READER MODE so all text I have typed when writing comment or email (using email website in my work) is LOST. Going back does not help, all text boxes are empty! You can not undo READER MODE without loosing all text typed in text fields. I am NOT writing about reloading page but about READER MODE switch, which is available on some pages.

Please help me disabling READER VIEW, I can not work now :(

I have found a solution:

set this pref to false on the about:config page to disable reader view.

   reader.parse-on-load.enabled = false 

but now I can not use reader view at all :(

Sometimes a page can intercept a keyboard shortcut and it will not reach Firefox. For example, Ctrl+b opens the Bookmarks Sidebar, but on some sites, it will bold text instead. Perhaps there is a way to intercept Alt+r with a script injected into the page (either by an add-on or in some other manner).

On U.S. English Firefox on Windows 7, Alt+R doesn't do anything; the shortcut for Reader View is Ctrl+Alt+R. But I might be able to create a script for you to test by working on a different shortcut. (Not right now, maybe overnight.)