Open a file in a tab in vim in readonly mode
To open a file in read only mode in a new tab, use
tab sview /path/to/file
To open the file in the same pane, (without using a new window or tab), use
view /path/to/file
Note that tab view /path/to/file does not open a new tab.
You can open a file in readonly mode from inside vim:
:view /path/to/file
or from command line:
$ vim -M /path/to/file