I started in "safe mode" and everything was responsive. Restarted and disabled all addons / plugins -> back to choppy.

 "application": {
   "name": "Firefox",
   "version": "38.0.1",
   "buildID": "20150513174244",
   "userAgent": "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0",
   "updateChannel": "release",
   "supportURL": "https://support.mozilla.org/1/firefox/38.0.1/WINNT/de/",
   "numTotalWindows": 1,
   "numRemoteWindows": 0,
   "remoteAutoStart": false
 },
 "crashes": {
   "submitted": [],
   "pending": 0
 },
 "modifiedPreferences": {
   "browser.cache.disk.smart_size.first_run": false,
   "browser.cache.disk.smart_size.use_old_max": false,
   "browser.cache.disk.capacity": 358400,
   "browser.cache.frecency_experiment": 1,
   "browser.download.importedFromSqlite": true,
   "browser.places.smartBookmarksVersion": 7,
   "browser.sessionstore.upgradeBackup.latestBuildID": "20150513174244",
   "browser.startup.homepage_override.mstone": "38.0.1",
   "browser.startup.homepage_override.buildID": "20150513174244",
   "dom.mozApps.used": true,
   "extensions.lastAppVersion": "38.0.1",
   "media.gmp-eme-adobe.lastUpdate": 1432155265,
   "media.gmp-gmpopenh264.lastUpdate": 1432155267,
   "media.gmp-gmpopenh264.version": "1.4",
   "media.gmp-eme-adobe.version": "9",
   "media.gmp-manager.lastCheck": 1432155248,
   "media.gmp-manager.buildID": "20150513174244",
   "network.cookie.prefsMigrated": true,
   "network.predictor.cleaned-up": true,
   "places.database.lastMaintenance": 1432156065,
   "places.history.expiration.transient_current_max_pages": 53646,
   "plugin.importedState": true,
   "plugin.disable_full_page_plugin_for_types": "application/pdf",
   "privacy.sanitize.migrateFx3Prefs": true,
   "storage.vacuum.last.places.sqlite": 1432156193,
   "storage.vacuum.last.index": 0
 },
 "lockedPreferences": {},
 "graphics": {
   "numTotalWindows": 1,
   "numAcceleratedWindows": 0,
   "windowLayerManagerType": "Basic",
   "windowLayerManagerRemote": true,
   "numAcceleratedWindowsMessage": [
     "tryNewerDriver",
     "9.6"
   ],
   "adapterDescription": "Standard-VGA-Grafikkarte",
   "adapterVendorID": "0x1002",
   "adapterDeviceID": "0x7145",
   "adapterSubsysID": "200617aa",
   "adapterRAM": "Unknown",
   "adapterDrivers": "vga framebuf vga256 vga64k",
   "driverVersion": "6.1.7600.16385",
   "driverDate": "6-21-2006",
   "adapterDescription2": "",
   "adapterVendorID2": "",
   "adapterDeviceID2": "",
   "adapterSubsysID2": "",
   "adapterRAM2": "",
   "adapterDrivers2": "",
   "driverVersion2": "",
   "driverDate2": "",
   "isGPU2Active": false,
   "direct2DEnabled": false,
   "directWriteEnabled": false,
   "directWriteVersion": "6.2.9200.17292",
   "direct2DEnabledMessage": [
     "tryNewerDriver",
     "9.6"
   ],
   "webglRendererMessage": [
     "tryNewerDriver",
     "9.6"
   ],
   "info": {
     "AzureCanvasBackend": "skia",
     "AzureSkiaAccelerated": 0,
     "AzureFallbackCanvasBackend": "cairo",
     "AzureContentBackend": "cairo"
   }
 },
 "javaScript": {
   "incrementalGCEnabled": true
 },
 "accessibility": {
   "isActive": false,
   "forceDisabled": 0
 },
 "libraryVersions": {
   "NSPR": {
     "minVersion": "4.10.8",
     "version": "4.10.8"
   },
   "NSS": {
     "minVersion": "3.18.1 Basic ECC",
     "version": "3.18.1 Basic ECC"
   },
   "NSSUTIL": {
     "minVersion": "3.18.1",
     "version": "3.18.1"
   },
   "NSSSSL": {
     "minVersion": "3.18.1 Basic ECC",
     "version": "3.18.1 Basic ECC"
   },
   "NSSSMIME": {
     "minVersion": "3.18.1 Basic ECC",
     "version": "3.18.1 Basic ECC"
   }
 },
 "userJS": {
   "exists": false
 },
 "extensions": [
   {
     "name": "Firefox Certificate Store Hotfix",
     "version": "20150311.01",
     "isActive": false,
     "id": "firefox-hotfix@mozilla.org"
   }
 ],
 "experiments": []

It's on windows 7, everything is choppy (opening menus, loading pages, opening new tabs, opening settings, ..) I started in "safe mode" and everything was responsive. Restarted and disabled all addons / plugins -> back to choppy. Deinstalled, renamed profile directory and restarted: Choppy again :( Any idea? I'm currently on Chrome for this question. If I could provide more information, please tell me. about:support gives these: { "application": { "name": "Firefox", "version": "38.0.1", "buildID": "20150513174244", "userAgent": "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0", "updateChannel": "release", "supportURL": "https://support.mozilla.org/1/firefox/38.0.1/WINNT/de/", "numTotalWindows": 1, "numRemoteWindows": 0, "remoteAutoStart": false }, "crashes": { "submitted": [], "pending": 0 }, "modifiedPreferences": { "browser.cache.disk.smart_size.first_run": false, "browser.cache.disk.smart_size.use_old_max": false, "browser.cache.disk.capacity": 358400, "browser.cache.frecency_experiment": 1, "browser.download.importedFromSqlite": true, "browser.places.smartBookmarksVersion": 7, "browser.sessionstore.upgradeBackup.latestBuildID": "20150513174244", "browser.startup.homepage_override.mstone": "38.0.1", "browser.startup.homepage_override.buildID": "20150513174244", "dom.mozApps.used": true, "extensions.lastAppVersion": "38.0.1", "media.gmp-eme-adobe.lastUpdate": 1432155265, "media.gmp-gmpopenh264.lastUpdate": 1432155267, "media.gmp-gmpopenh264.version": "1.4", "media.gmp-eme-adobe.version": "9", "media.gmp-manager.lastCheck": 1432155248, "media.gmp-manager.buildID": "20150513174244", "network.cookie.prefsMigrated": true, "network.predictor.cleaned-up": true, "places.database.lastMaintenance": 1432156065, "places.history.expiration.transient_current_max_pages": 53646, "plugin.importedState": true, "plugin.disable_full_page_plugin_for_types": "application/pdf", "privacy.sanitize.migrateFx3Prefs": true, "storage.vacuum.last.places.sqlite": 1432156193, "storage.vacuum.last.index": 0 }, "lockedPreferences": {}, "graphics": { "numTotalWindows": 1, "numAcceleratedWindows": 0, "windowLayerManagerType": "Basic", "windowLayerManagerRemote": true, "numAcceleratedWindowsMessage": [ "tryNewerDriver", "9.6" ], "adapterDescription": "Standard-VGA-Grafikkarte", "adapterVendorID": "0x1002", "adapterDeviceID": "0x7145", "adapterSubsysID": "200617aa", "adapterRAM": "Unknown", "adapterDrivers": "vga framebuf vga256 vga64k", "driverVersion": "6.1.7600.16385", "driverDate": "6-21-2006", "adapterDescription2": "", "adapterVendorID2": "", "adapterDeviceID2": "", "adapterSubsysID2": "", "adapterRAM2": "", "adapterDrivers2": "", "driverVersion2": "", "driverDate2": "", "isGPU2Active": false, "direct2DEnabled": false, "directWriteEnabled": false, "directWriteVersion": "6.2.9200.17292", "direct2DEnabledMessage": [ "tryNewerDriver", "9.6" ], "webglRendererMessage": [ "tryNewerDriver", "9.6" ], "info": { "AzureCanvasBackend": "skia", "AzureSkiaAccelerated": 0, "AzureFallbackCanvasBackend": "cairo", "AzureContentBackend": "cairo" } }, "javaScript": { "incrementalGCEnabled": true }, "accessibility": { "isActive": false, "forceDisabled": 0 }, "libraryVersions": { "NSPR": { "minVersion": "4.10.8", "version": "4.10.8" }, "NSS": { "minVersion": "3.18.1 Basic ECC", "version": "3.18.1 Basic ECC" }, "NSSUTIL": { "minVersion": "3.18.1", "version": "3.18.1" }, "NSSSSL": { "minVersion": "3.18.1 Basic ECC", "version": "3.18.1 Basic ECC" }, "NSSSMIME": { "minVersion": "3.18.1 Basic ECC", "version": "3.18.1 Basic ECC" } }, "userJS": { "exists": false }, "extensions": [ { "name": "Firefox Certificate Store Hotfix", "version": "20150311.01", "isActive": false, "id": "firefox-hotfix@mozilla.org" } ], "experiments": [] }