fixes #16255

src/vs/workbench/parts/git/common/gitContentProvider.ts

@@ -45,7 +45,7 @@ export class GitContentProvider implements IWorkbenchContribution, ITextModelCon
 			}
 
 			const path = uri.fsPath;
-			const relativePath = paths.relative(root, path);
+			const relativePath = paths.relative(root, path).replace(/\\/g, '/');
 			const treeish = gitModel.getStatus().find(relativePath, StatusType.INDEX) ? '~' : 'HEAD';
 
 			return this.gitService.buffer(path, treeish)

src/vs/workbench/parts/git/node/rawGitService.ts

@@ -189,7 +189,7 @@ export class RawGitService implements IRawGitService {
 		treeish = (!treeish || treeish === '~') ? '' : treeish;
 
 		if (isAbsolute(filePath)) {
-			filePath = relative(this.repo.path, filePath);
+			filePath = relative(this.repo.path, filePath).replace(/\\/g, '/');
 		}
 
 		return this.repo.buffer(treeish + ':' + filePath).then(null, e => {