Your System Details shows;

Installed add-on

75cbd746-59b2-4036-ad81-08dfd29d463b What is this ?

Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

I honestly do not know what that add-on is. I do not see it under "Extensions". No luck with your suggested safe mode workaround. The setting does not change anything. Web content is fine, just the text in the sidebar is affected.

Type about:support in the address bar and press Enter.

Now press <Control>(Mac:<Command>) F to bring up the search bar. Now search for 08dfd29d463b If something is found, copy the information and post it in the reply box.

If nothing is found, go to about:plugins and try again.

unfortunately that's all that's there!

I've called the big guys to help you. For now, disable it.

Start your Computer in safe mode. Then start Firefox. Try Safe web sites.

Starting The Computer In Safe Mode;
Free Online Encyclopedia

you know what? i found a solution by pure coincidence. the problem goes away instantly if i tick "reduce transparency" in system preferences of OS 10.10.

p.s. how can i get rid of this mysterious extension if it's not listed?

Open the Add-ons Manager. Look around and if you find it, Take a snap.

If you mean "tools" -> "addons" you should re-read the conversation before. It does not show up there. Only via "about:support". And it's just a mysterious number.

I have this problem too. Everything is nice in FF 33.1.1 (and lower versions) but fonts look ugly in FF 34.0.5 (and beta versions of FF 35 I tried). And NO, that doesn't refer to any extensions, really. I disabled all extensions, same issue. I even uninstalled all extensions to check and then downloaded fresh version of FF (34.0.5) — same issue! This is critical to me, I can't look at this ****. Neighter I want to use "Decrease transparency" in system-wide Accessibility settings, nor I want to disable font smoothing system-wide ("Use LCD font smoothing when available" setting). BTW, if font smoothing is disabled system-wide then FF 34 looks better compared to when this setting is enabled (so AA works in FF 34, but works in an awful way), but all apps (including FF 33) look better on my system with font smoothing enabled.

prime1122 Please go to the top of any support.mozilla.org web page and use the Ask A Question link; https://support.mozilla.org/en-US/questions/new This will let us look at your system details. No Personal Information Is Collected.

hexeric Unless someone shows up to identify that extension, I recommend resetting FF.

Reset Firefox {web link} is a LAST RESORT ! !

Reset Firefox -- easily fix most problems

If you're having problems with Firefox, resetting it can help. The reset feature fixes many issues by restoring Firefox to its factory default state while saving your essential information like bookmarks and open tabs.

Done: https://support.mozilla.org/en-US/questions/1035963

I'm obviously on FF 33.1.1 since I can't stand how 34+ looks. Have a look at extensions list if you need to but that's NOT about extensions, it's a FF issue.

prime1122 This thread was closed

FredMcD, I'm cool with that. Do you still need any environment information to trace the problem down?

Here's my info. Everything works alright with version 33.1.1 but turns ugly in terms of fonts look if I upgrade higher.

{

 "application": {
   "name": "Firefox",
   "version": "33.1.1",
   "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:33.0) Gecko/20100101 Firefox/33.0",
   "supportURL": "https://support.mozilla.org/1/firefox/33.1.1/Darwin/ru/",
   "numTotalWindows": 29,
   "numRemoteWindows": 0
 },
 "crashes": {
   "submitted": [],
   "pending": 0
 },
 "modifiedPreferences": {
   "accessibility.typeaheadfind.flashBar": 0,
   "browser.cache.disk.smart_size.first_run": false,
   "browser.cache.disk.enable": false,
   "browser.cache.frecency_experiment": 3,
   "browser.cache.disk.smart_size.use_old_max": false,
   "browser.cache.disk.capacity": 358400,
   "browser.places.smartBookmarksVersion": 7,
   "browser.search.useDBForOrder": true,
   "browser.sessionstore.upgradeBackup.latestBuildID": "20141113143407",
   "browser.startup.homepage_override.mstone": "33.1.1",
   "browser.startup.homepage": "about:newtab",
   "browser.startup.homepage_override.buildID": "20141113143407",
   "browser.tabs.warnOnOpen": false,
   "browser.tabs.warnOnClose": false,
   "dom.mozApps.used": true,
   "extensions.lastAppVersion": "33.1.1",
   "font.internaluseonly.changed": true,
   "media.gmp-gmpopenh264.lastUpdate": 1414213076,
   "media.gmp-gmpopenh264.version": "1.1",
   "media.gmp-manager.lastCheck": 1418361230,
   "network.cookie.prefsMigrated": true,
   "places.history.expiration.transient_current_max_pages": 104858,
   "places.database.lastMaintenance": 1418361248,
   "plugin.importedState": true,
   "plugin.disable_full_page_plugin_for_types": "application/pdf",
   "plugin.state.adobepdfviewernpapi": 0,
   "privacy.sanitize.migrateFx3Prefs": true,
   "storage.vacuum.last.index": 1,
   "storage.vacuum.last.places.sqlite": 1417605925
 },
 "lockedPreferences": {},
 "graphics": {
   "numTotalWindows": 29,
   "numAcceleratedWindows": 29,
   "windowLayerManagerType": "OpenGL",
   "windowLayerManagerRemote": true,
   "adapterDescription": "",
   "adapterVendorID": "0x10de",
   "adapterDeviceID": "0x11c2",
   "adapterRAM": "",
   "adapterDrivers": "",
   "driverVersion": "",
   "driverDate": "",
   "webglRenderer": "NVIDIA Corporation -- NVIDIA GeForce GTX 650 Ti BOOST OpenGL Engine",
   "info": {
     "AzureCanvasBackend": "quartz",
     "AzureSkiaAccelerated": 0,
     "AzureFallbackCanvasBackend": "none",
     "AzureContentBackend": "quartz"
   }
 },
 "javaScript": {
   "incrementalGCEnabled": true
 },
 "accessibility": {
   "isActive": false,
   "forceDisabled": 0
 },
 "libraryVersions": {
   "NSPR": {
     "minVersion": "4.10.7",
     "version": "4.10.7"
   },
   "NSS": {
     "minVersion": "3.17.2 Basic ECC",
     "version": "3.17.2 Basic ECC"
   },
   "NSSUTIL": {
     "minVersion": "3.17.2",
     "version": "3.17.2"
   },
   "NSSSSL": {
     "minVersion": "3.17.2 Basic ECC",
     "version": "3.17.2 Basic ECC"
   },
   "NSSSMIME": {
     "minVersion": "3.17.2 Basic ECC",
     "version": "3.17.2 Basic ECC"
   }
 },
 "userJS": {
   "exists": false
 },
 "extensions": [
   {
     "name": "Менеджер сессий",
     "version": "0.8.1.6",
     "isActive": true,
     "id": "{1280606b-2510-4fe0-97ef-9b5a22eafe30}"
   },
   {
     "name": "Adblock Plus",
     "version": "2.6.6",
     "isActive": true,
     "id": "{d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}"
   },
   {
     "name": "Bookmark Current Tab Set",
     "version": "0.2.4",
     "isActive": true,
     "id": "bookmarkcurrenttabset@jake.kasprzak.ca"
   },
   {
     "name": "Bookmark Duplicate Cleaner",
     "version": "0.2",
     "isActive": true,
     "id": "bookmarkdup@localghost.net"
   },
   {
     "name": "Classic Theme Restorer (Customize UI)",
     "version": "1.2.6.1",
     "isActive": true,
     "id": "ClassicThemeRestorer@ArisT2Noia4dev"
   },
   {
     "name": "EPUBReader",
     "version": "1.4.2.6",
     "isActive": true,
     "id": "{5384767E-00D9-40E9-B72F-9CC39D655D6F}"
   },
   {
     "name": "Firebug",
     "version": "2.0.7",
     "isActive": true,
     "id": "firebug@software.joehewitt.com"
   },
   {
     "name": "FlashGot",
     "version": "1.5.6.8",
     "isActive": true,
     "id": "{19503e42-ca3c-4c27-b1e2-9cdb2170ee34}"
   },
   {
     "name": "Go Parent Folder",
     "version": "2.9.1",
     "isActive": true,
     "id": "goParentFolder@alice"
   },
   {
     "name": "RESTClient",
     "version": "2.0.3",
     "isActive": true,
     "id": "{ad0d925d-88f8-47f1-85ea-8463569e756e}"
   },
   {
     "name": "SaveFrom.net помощник",
     "version": "3.70",
     "isActive": true,
     "id": "helper@savefrom.net"
   },
   {
     "name": "Show Parent Folder",
     "version": "2.1",
     "isActive": true,
     "id": "showParentFolder@alice"
   },
   {
     "name": "Tab Mix Plus",
     "version": "0.4.1.5.2",
     "isActive": true,
     "id": "{dc572301-7619-498c-a57d-39143191b318}"
   },
   {
     "name": "Tamper Data",
     "version": "11.0.1",
     "isActive": true,
     "id": "{9c51bd27-6ed8-4000-a2bf-36cb95c0c947}"
   },
   {
     "name": "Troubleshooter",
     "version": "1.1a",
     "isActive": true,
     "id": "troubleshooter@mozilla.org"
   },
   {
     "name": "Vacuum Places Improved",
     "version": "1.2",
     "isActive": true,
     "id": "VacuumPlacesImproved@lultimouomo-gmail.com"
   },
   {
     "name": "Xmarks",
     "version": "4.3.5",
     "isActive": true,
     "id": "foxmarks@kei.com"
   },
   {
     "name": "Pushbullet",
     "version": "38",
     "isActive": false,
     "id": "jid1-BYcQOfYfmBMd9A@jetpack"
   },
   {
     "name": "UrlCorrector",
     "version": "0.5.7",
     "isActive": false,
     "id": "urlcorrector@durilka.com"
   }
 ],
 "experiments": []

}