i have firefox as a favorite and because i used profile manager it starts with choose profile dialog... but only the first time... if i try to open a second instance from favorites then the choose profile does not come up... i think i have to add "no-remote" to exec but i dont know where to do it... "no-remote" as search term here doesnt work as expected... thanks

Program starters are .desktop files, like "firefox.desktop". Usually in "/usr/share/applications" or "/home/<username>/.local/share/applications". To add a second firefox starter for your second profile:

1. Find the original firefox starter desktop file.
2. Make a copy of it, with a different file name like "firefox2.desktop" in "/home/<username>/.local/share/applications".
3. Open this copy with a text editor. Replace the value for "Name" with something to make it distinguishable, and append the firefox options to the value for "Exec". Like so:

4. Wait for your desktop/startmenu/taskbar/search function to recognize the new file. You should now have an additional firefox entry in your startmenu/taskbar/search function.

You can also one-time launch a firefox with second profile from the command line:
or

the "%u" looks like a substitution variable in the "exec" line. Is it possible to substitute "--no-remote" into %u somewhere when I want to instead of creating another .desktop file? thanks.

you can create your own desktop files as you see fit.

i was unclear... i wonder if it is possible to enter a value for "%u" somehow in another script or dialog and use THIS desktop item with the substituted argument... if "%u" is a variable then where is it set? can i set it without editing THIS desktop file?

yes, you can copy THIS desktop file to a new version of itself and do your edits.

sorry, maybe i'm being thick, i must admit i had difficulty following your problem description from the start.

I guess a lot of people dont use this firefox feature... i use it to prevent any cross-window interactions from sketchy websites... i use noscript but dont want to use it all the time or keep turning it on and off and forgetting etc... so i have different profiles for trusted and untrusted browsing etc... anyway i tried to create new desktop file with --no-remote on exec line but it still doesnt bring up choose user profile dialog for second instance... i saw this "bug" on the web but hoped these were all old posts and the problem had been resolved... i tried putting -no-remote before and after %u... also with and without -P also tried --no-remote (2 dashes)... nothing works... or maybe i missed the correct combination

1. use profile manager to create multiple profiles
2. select a default profile for firefox in profile manager
3. enter "about: profiles" as home page in fire fox default profile
4. about: profiles lets you launch separate instances of firefox with separate profiles
(it wont let you have 2 instances of same profile... same as in past)

if anyone figures out how to configure firefox to launch profile manager with each instance please post here. thanks.