Import .JSON fails to work.

[DaveF63]

Hi
I'm having problems importing .JSON files.

Using latest Firefox/Edge browsers

I open C:\Users\X\Potlatch\user_state.sol. It appears to load as expected. I'm able to view all the nodes/children as expected.

I click on Export. It downloads a file:
C:\Users\X\Download\user_state
(Edge browser exports the file with a .txt extension.)

Without amending it, I Import it by pasting the file path & clicking on the red 'IMPORT' button & the border of box which has 'Valid JSON' within it turns red. I presume the file's content is meant to appear there. I click the 'X' to close that & another window with 'Notice, Please enter valid JSON' appears.

I've validated the json file in an online test page.
I tried changing the extension to .json, but with no luck.
What am I misunderstanding?

{"overpass_query":"[out:json][bbox:51.2892,-2.5241,51.4691,-2.236];\rway[railway=platform];\rout center","overview_tiles":"https://tile.openstreetmap.org/","simplify_tolerance":0.00005,"F1":{"value":"train=yes; ref=Earl's Halt; railway=platform","code":"Saved tags"},"background_dim":true,"help_shown":"true","api":"https://www.openstreetmap.org/api/0.6/","background_url":"https://ecn.t{switch:0,1,2,3}.tiles.virtualearth.net/tiles/a{quadkey}.jpeg?g=587&mkt=en-gb&n=z","background_name":"Bing Maps Aerial","stylesheet_url":"stylesheets/potlatch.css","bookmarks":[{"lon":0,"name":"Wellow","lat":0},{"lon":-2.351416681289673,"name":"Roundabout","lat":51.38420829895039},{"lon":-2.42849,"name":"Peasedown","lat":51.3151883235235},{"lon":-2.448145227661133,"name":"Radstock","lat":51.2921443982106},{"lon":-2.4810574413299564,"name":"MSN","lat":51.286890753111976},{"lon":-2.317599617385864,"name":"Batheaston","lat":51.40599991940916}],"close_changesets":false,"stylesheet_name":"Potlatch","background_sharpen":true}