Mint 18.1, a few apps started showing different cursor - pointer, link selection, busy / window loading (some spinning do-dad). Most still use the theme I installed a few yrs ago ("superme-series-master" - red theme).

Tor Browser started using very tiny black pointer - even over black areas. I believe TBB is mostly GTK3 (based on Fx 68.x ESR). The other icons it uses are too small or same color as the BG. I tried the Cinnamon Settings - enlarge pointer size - didn't change anything in TBB.

Other apps that don't use the selected theme (but don't all necessarily use the SAME un-selected theme)
- SMPlayer - don't know if it switched to GTK3, but other GTK2 apps use the selected superme theme OK.

- VLC player - don't know what theming engine it uses, but it always used the selected cursor.

Most other apps I checked were fine - GTK2 & GTK3. Too many to check now.

Any ideas why less than a handful are protesting?
If TBB was on board, I might forget about the other few.

I used a search tool on Tor Browser's directory - even extracted omni.ja. Found no cursor files.

The few questions I found about this usually involved way more - or most apps.
Thanks.

I am using xubuntu but I expect this fix will work in mint also. If not just delete the file you made. Ubuntu has been notorious for this long standing bug. Create a text file called .Xresources (note that is a capital X). Put this in the file:

Xcursor.size: 48
Xcursor.theme: DMZ-Black

Of course you put the proper color and size you always want. Works like a charm for me across many computers.

Thanks, cmcanulty.
The long standing bug being, that only a few apps suddenly stop using the selected cursor theme?
To your knowledge, has anyone ever found the cause of this, if not a permanent fix?

Does my cursor theme being in ~/.themes have a bearing on where file .Xresources is placed?
I've read some comments suggesting to add the desired cursor theme name (some say the whole path) in /usr/share/.icons/default. Entering the path & file name didn't work here, after a restart. Others said they didn't use the full path - just theme name. Don't remember if they had some of their cursor themes in ~/.themes.

Still others said they put custom cursor themes in /.themes & /usr/share/.icons. I've tried that w/ custom Mint themes to see if some problem persisted. But, you have to name any theme in Mint 18 (I think 19), as the themes settings UI - Cinnamon in LM 18.1 - doesn't say where each theme is installed.

You didn't say where to place the .Xresources file.
By the period, it looks like in root (base) directory of /home.

There is a directory, "/etc/X11/Xresources" that contains one file, x11-common. Which is odd - the filename you mention could possible be a single user version of the file?
Maybe the same file in /etc/x11/Xresources, for global use? Just a guess.

Sorry yes put it in your home folder. this works for me in everything.Doing it in themes did nothing for me.I spent so much time figuring this out that I just put it in any and all /home/.Xresources as it works in every app for me.

Problem is solved - mostly. Sorry, but in Mint 18.1, creating .Xresources file in my /Home/user directory didn't work. I found more info online about that method & tried a few different things with it - none worked.

The solution was fairly simple, once I figured it out. That's like saying, "I found my missing (xyz) in the last place I looked."
Now, even apps running under Wine use the custom cursor theme.

The problem seemed mostly permissions (in /usr/share/icons) on the "cursors" folder, under the top folder with custom cursor theme name; and maybe?? Mint / Cinnamon expecting the index.theme file to contain "Inherits=<theme-name>" (in /usr/share/icons/default).

Permissions on all cursor images files matched the other cursor themes. Possibly, the permissions on "cursors" folder in the theme may have stopped Tor Browser from using the theme. Because, if I selected another native or repo-installed cursor theme in Settings> Themes> "mouse pointer" (in Mint w/ Cinnamon), TBB used them OK, whether or not they were listed in theme "default" folders.

I compared permissions on all the custom cursor theme's folders & files to repo installed cursor themes (like DMZ-White) & changed the custom theme's permissions to match.
The custom cursor theme was just a .zip file (as many are) & instructions on this type of theme were to extract it to /usr/share/icons (destination opened as root, I assume). or for just one user, to the ~/.icons folder (create it if missing). But that wasn't Tor Browser's problem.

I noticed (& several tutorials mentioned) that many custom cursor themes - NOT from your repo, often have BOTH the cursor.theme & index.theme files.
Several claimed the file placed in "default" folder had to be "index.theme." Now, I'm not sure that matters.
In fact, both DMZ-Black & DMZ-White - just reinstalled from Mint repo, have both those files; in both themes, the "cursor.theme" file has: "Inherits=DMZ-Black", etc.

And both DMZ themes work fine, so maybe in MY distro & DE, it doesn't matter if the file name in /usr/share/icons/default (or ~/.icons/default) is index.theme or cursor.theme.
In this custom cursor theme & others I checked, the cursor.theme file has the data:
like:
I imagine capitalization & spacing matters for the theme name.

The problem with Mint-Cinnamon (maybe other distros & DEs), if you want one cursor theme to be default, many said you HAVE to use /usr/share/icons/default folder AND Mint and/or Cinnamon wants the index.theme file in /usr/.../default folder to contain, "Inherits=<theme-name>". I'm not sure of that.
It's possible that the value Cinnamon stores in dconf under "org.cinnamon.desktop.interface" is treated as default cursor theme. The theme I select in Settings > Theme > mouse pointer, is what shows in the dconf path, as "cursor-theme." But cursor theme folder / file permission issues may stop certain apps from using the default theme.

I copied the cursor.theme file to /usr/share/icons/default, then changed file name to Index.theme.
As many suggested, I created a "default" folder under ~/.icons/default and changed the file name under ~/.icons/default to index.theme. Again, I'd have to test if the file under /default folders being named matters - I'd have to test it.

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