patch from community member -- untested

src/scripts/background.js

@@ -146,6 +146,7 @@ function proxyRequest(requestInfo) {
 
 function setActiveSettings(settings) {
   browser.proxy.onRequest.hasListener(proxyRequest) && browser.proxy.onRequest.removeListener(proxyRequest);
+  browser.webRequest.onBeforeSendHeaders.hasListener(check_proxy) && browser.webRequest.onBeforeSendHeaders.removeListener(check_proxy);
 
   const pref = settings;
   const prefKeys = Object.keys(pref).filter(item => !['mode', 'logging', 'sync'].includes(item)); // not for these
@@ -186,6 +187,7 @@ function setActiveSettings(settings) {
       activeSettings.proxySettings[idx].whitePatterns = processPatternObjects(activeSettings.proxySettings[idx].whitePatterns);
     }
     browser.proxy.onRequest.addListener(proxyRequest, {urls: ["<all_urls>"]});
+    browser.webRequest.onBeforeSendHeaders.addListener(check_proxy, {urls: ["<all_urls>"]}, ["blocking", "requestHeaders"]);    
     Utils.updateIcon('images/icon.svg', null, 'patterns', 'patterns');
     console.log(activeSettings, "activeSettings in patterns mode");
   }
@@ -195,6 +197,7 @@ function setActiveSettings(settings) {
     if (settings[mode]) {
       activeSettings.proxySettings = [settings[mode]];
       browser.proxy.onRequest.addListener(proxyRequest, {urls: ["<all_urls>"]});
+      browser.webRequest.onBeforeSendHeaders.addListener(check_proxy,{urls: ["<all_urls>"]}, ["blocking", "requestHeaders"]);
       Utils.updateIcon('images/icon.svg', settings[mode].color, 'forAll', true, Utils.getProxyTitle(settings[mode]), false);
       console.log(activeSettings, "activeSettings in fixed mode");      
     }
@@ -212,6 +215,7 @@ function setActiveSettings(settings) {
 
 function setDisabled(isError) {
   browser.proxy.onRequest.hasListener(proxyRequest) && browser.proxy.onRequest.removeListener(proxyRequest);
+  browser.webRequest.onBeforeSendHeaders.hasListener(check_proxy) && browser.webRequest.onBeforeSendHeaders.removeListener(check_proxy);
   chrome.runtime.sendMessage({mode: 'disabled'});           // Update the options.html UI if it's open
   Utils.updateIcon('images/icon-off.svg', null, 'disabled', true);
   console.log('******* disabled mode');
@@ -220,8 +224,19 @@ function setDisabled(isError) {
 
 // ----------------- Proxy Authentication ------------------
 // ----- session global
-let authData = {};
+// stopp using authData in its current implementation - we are using "proxy_for_requestID" now
+//let authData = {};
 let authPending = {};
+let proxy_for_requestID = {};
+
+// Might be set from GUI in future, if feature gets implemented:
+let force_global_reauth = false;
+let force_global_reauth_username = '';
+
+function reset_global_reauth() {
+  force_global_reauth = false;
+  force_global_reauth_username = '';
+}
 
 async function sendAuth(request) {
   // Do nothing if this not proxy auth request:
@@ -274,4 +289,112 @@ function clearPending(request) {
   }
 
   delete authPending[request.requestId];                    // no error
-}
+}
+
+// Work around bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1510510
+//  Should force reauthentication for http-proxy:
+//  - using digest authentication after changing the username
+//  - using basic authentication after changing the username and/or password.
+//  Does not work until browser establishes new connection to proxy.
+//  Established TCP connections might need to be closed first (keep-alive has to expire).
+//
+//  This works by examining the headers sent by the browser and deleting the
+//  authentication header if it doesn't seem to match what the current
+//  FoxyProxy configuration expects.
+//
+//  Browser does not always fires "onAuthRequired" and asks extensions to provide
+//  auth credentials, if he has some (working) credentials cached. Therefore
+//  an extension has no chance to make the browser aware of edited
+//  username/password. This applies for different pattern based proxy
+//  configurations as well, where address and port of proxies are the same but
+//  the user wants to (or has to) use differnt username/password based on some
+//  pattern in FoxyProxy, if he enables/disables a proxy config inside FoxyProxy
+//  or if he changes the order of proxy configs.
+//  Browser will keep using the first working proxy, at least until proxy
+//  refuses CONNECT, while FoxyProxy shows in her gui that the correct proxy was
+//  used. Actually FoxyProxy can not know which proxy config with same
+//  address/port is used, if it was not asked for auth credentials.
+//
+//  This check gives user the chance to edit/correct credentials or invalidate
+//  credentials that were sent before (and accepted by proxy) via FoxyProxy
+//  without having to restart the browser.
+//  But this might be considered expensive (header check runs for every
+//  request), especially if no authentication is used.
+//  So it might be useful to provide a switch in the gui to pref this check on/off.
+//
+//  Further tests and improvements welcome!
+
+function check_proxy(request) {
+  var asyncRewrite = new Promise((resolve, reject) => {
+    let send_original_headers = false;
+    let new_requestHeaders = [];
+    if (!proxy_for_requestID[request.requestId]) {
+      send_original_headers = true;
+    } else if (!proxy_for_requestID[request.requestId].username) {
+      send_original_headers = true;
+    } else if (!request.proxyInfo) {
+      send_original_headers = true;
+    } else if (request.proxyInfo.type == "http") {
+      for (var header of request.requestHeaders) {
+        if (header.name.toLowerCase() === "proxy-authorization") {
+          let force_rauth = false;
+          const headerValues = header.value.split(",");
+          for (var i=0; i<headerValues.length; i++) {
+            if (headerValues[i].startsWith("Digest username=")) {
+              let digestUsername_pre = headerValues[i].split("Digest username=");
+              if (digestUsername_pre.length >= 1) {
+                let digestUsername = "";
+                for (var j=0; j<digestUsername_pre[1].length; j++) {
+                  let char = digestUsername_pre[1][j];
+                  if (char != '"' && char != '\\') {
+                    digestUsername += char;
+                  }
+                }
+                if (digestUsername != proxy_for_requestID[request.requestId].username) {
+                  force_rauth = true;
+                } else if (force_global_reauth && force_global_reauth_username != "" && force_global_reauth_username == proxy_for_requestID[request.requestId].username) {
+                  force_rauth = true;
+                  reset_global_reauth();
+                }
+              }
+              break;
+            } else if (headerValues[i].startsWith("Basic ")) {
+              let basicAuth_pre = headerValues[i].split("Basic ");
+              if (basicAuth_pre.length >= 1) {
+                let basicAuthClear = proxy_for_requestID[request.requestId].username + ":" + proxy_for_requestID[request.requestId].password;
+                let credentials_planned = window.atob(basicAuth_pre[1]);
+                // not used
+                //let credentials_planned_list = credentials_planned.split(":");
+                if (basicAuthClear != credentials_planned) {
+                  force_rauth = true;
+                } else if (force_global_reauth && force_global_reauth_username != "" && force_global_reauth_username == proxy_for_requestID[request.requestId].username) {
+                  force_rauth = true;
+                  reset_global_reauth();
+                }
+              }
+              break;
+            }
+          };
+          if (!force_rauth) {
+            new_requestHeaders.push(header);
+          }
+        } else {
+          new_requestHeaders.push(header);
+        }
+      }
+    } else {
+      send_original_headers = true;
+    }
+    if (send_original_headers) {
+      new_requestHeaders = request.requestHeaders;
+    }
+    resolve({requestHeaders: new_requestHeaders});
+  });
+  return asyncRewrite;
+}
+
+function clearProxyrRequestID(request) {
+
+ if (proxy_for_requestID[request.requestId]) {
+   delete proxy_for_requestID[request.requestId];
+ }